Where does the term 'grand' come from?

I've not been able to answer your question but here are a few other interesting slang names for money.

Denominations of Money:
Slang term Amount
bob shilling [A bob was a money collection where participants put in a shilling each, usually for drinks. The expression then arose "to get your two bob's worth" which meant something was very good value, Aussies being fond of the occasional ale. - this possible explanation is courtesy of Dracos]
grand £1000
monkey £500
pony £25
tanner sixpence. Nick Arrow offers the following: from India - a rupee was about equal to a shilling, and was divided into sixteen annas. so half a rupee was "eight anna" - say it fast. or in Hindi, it's "aat anna". makes you jump when you hear it in India!
tenner £10 [Also known as a Paul McKenna (famous hypnotist). Thanks to Richard Hall]
tilbury sixpence
score £20 (Rhyming slang reference is apple core - see rhyming slang pages)
Oxford 5 shillings or a crown [derived from Oxford Scholar which rhymes with dollar which, pre-war, was just under 5 shillings - thanks to Jim Williams. Also known as Coachwheel]
'alf an Oxford 2 shillings & 6 pence or half a crown [Thanks to Jim Williams)
Nicker or Quid £1 [Thanks to Jim Williams. Also, the rhyming slang Bin Lid is used for quid - Thanks to Richard Hall]
Readies (Nelson Eddy's) Pound note [Thanks to Julia Jones - Colin Craig adds the following: Actually I believe "reddies" refers to £50 notes which are of course red. This term can be used to describe any amount of money. And Mark adds: A traditional term for cash is "ready money" a term still used on Smithfield market. I would suggest that this is where the term "reddies" comes from. Frank Wales advises that the term Nelsons refers to money generally, so a lot of nelsons is a lot of money]
Ton £100
Century £100 [John knows the expression C-Note, which he believes is American ]
Skin Diver (or Deep Sea Diver or Sky Diver or Scuba Diver or Pam Shriver) fiver [Lend us a deep sea 'til payday. Thanks to Peter Barnes and Paul Liney and Simon Rowan and Dean]
Sprarsy Anna Tanner (sixpence) [Lend us a sprarsy. Thanks to Mike Smith... he wonders if Sprarsy might have something to do with the old Indian coin called an "anna". If you have any more info please let me know]
Bullseye £50 [Thanks to Jez Stacey]
Wicker Basket £15. Neal says he's not sure of the origin although it has been suggested that it has something to do with flower sellers and Jack the Ripper (?). [Thanks to Neal Gordon]
Lady Godiva £5 (fiver). [Usage - 'ere, can you spare a lady?" Thanks to Jon Lord]
Ayrton Senna £10 (tenner). Also known as Louise Wener. See the rhyming slang tables. [Thanks to Jon Lord. Tom Good reports that he's also heard the phrase "Dead Brazilian" used, as in "I pulled a dead Brazilian out of me sky rocket"]
Plenty £20 [Reported to be not widely used. Thanks to Jon Lord]
Thrifty £50 [Reported to be not widely used. Thanks to Jon Lord]
One-er £100 [Pronounced "wunner". Thanks to Loz Grey]
Mother Hen £10 [Thanks to Loz Grey]
Archer £2000 [Based on the (alleged) amount Lord Jeffery Archer handed a prostitute, can't remember why but there was (again, allegedly) something dodgy about it. Thanks to Alan S. Greer]
Nugget £1 [Apparently because it's golden coloured. Thanks to Oliver Campion. Also known as Canary or Yellow-Boy. Shane Greyvenstein correctly points out that a yellow-boy, which is slang for guinea, is actually worth one pound, one shilling. I should note that when the guinea was originally struck in 1663 it was actually worth one pound - it wasn't until 1717 that the value was raised.]
Plum £100,000
Squid Quid [Jon Simmons reports this is commonly used in Reading]
Cock and Hen £10 [Thanks to Philip Hart and Bill Medhurst. Gareth adds that cockle is commonly used, as in "lend us a cockle".]
Wedge Comes from when coins could be split into quarters so exact weights could be measured. The shape of these sections was a wedge. [Thanks to Philip Hart]
Bottle £2 or £200 [Thanks to Bill Medhurst. Kris Johnson says this is from 'bottle of glue' -> two]
Carpet £3 or £300 [Thanks to Bill Medhurst. Kris Johnson says that prisoners used to get a square of carpet after being locked up for three years]
Rofe £4 or £400 (supposedly four backwards) [Thanks to Bill Medhurst]
Jacks Alive £5 [Thanks to Bill Medhurst]
Tom Mix £6 [Thanks to Bill Medhurst]
Nevis £7 (Seven backwards) [Thanks to Bill Medhurst]
Poorly Fish Six quid (sick squid) [Thanks to Kevin Lowther - sounds like more of a bad pun than slang but ... Tom reports that the reference he knows is "dead octopus" as in "I've only been here 5 minutes and I've done a dead octopus". And Darryl Clark reports the expression "dodgy octopus" is also used.]
Pavarotti (tenor) Tenner - £10 [Thanks to Dave Reynolds. Also referred to as a Lucy, according to Tom Harris]
Rocket £5 - from the picture of George Stevenson's rocket on the five pound note - thanks to Chris Kenny
Commodore £15 - how odd... Benjamin Preston says that this one derives from the fact that the Commodores sang "Three Times a Lady" (Lady Godiva - fiver)
Nifty £50 [Nifty - Fifty. Thanks toTim Le Maire]
Bag of Sand £1000 (grand) [Thanks to Keith Cole]
Bernie £1,000,000 [Refers to Bernie Ecclestone of Formula One fame who donated one million pounds to the Labour election campaign - thanks to Vidar Thomas Endresen]
Jackson £5 [From the Jackson Five - thanks to Steve Hicks]
Long 'un £100 [Thanks to Dean Willingham]
Bag (of sand) £1000 [Bag of Sand -> Grand. Thanks to Dean Willingham]
Dirty £30 [Thanks to Stuart McHugh]
Ching £5 [From the Spanish cinco perhaps. Thanks to Simon Mahon]
Maggie One pound coin - As in Maggie Thatcher (under whose premiership they were introduced, I believe), because "They're brassy and think they're a sovereign." [Thanks to Justyn Olby]
McGiver £5 [From the popular TV series - thanks to Ben Dellow]
Melvin £5 [From Howard Melvin and the Bluenotes - thanks to Rob Neal]
Browny £10 [Thanks to Kieren]
Edge Pence 20p [From the shape of the coin - thanks to Kieren]
McGarret £50 [From the Hawaii-50 television series. Thanks to Simon Mahon. Justin Soloman says the expression 'Jack Lord' is also used.]
Bar £1,000,000 [Thanks to Laurence Coley who says it's commonly used in the money markets and thinks the origin might have originated with the value of a bar of gold - uncertain. Ben Morton offers: I suggest it's because there's a bar on top of the "M" in its roman numeral equivalent. William Foot believes it should be £10,000,000.00. If anyone can clarify this I'd appreciate it.]
Alan £1 [From Alan Wicker - Thanks to Lee Newman]
Spanner 50p [Source might be due to the shape of the 50p - Thanks to Lee Newman. Chris offers the following "supporting evidence": Why does a fifty pence piece have flat sides? So you can use a spanner to get 'em out of a Scotsman's/ Aberdonian's/Yorkshireman's hand.]
Bobby Moore Score (i.e. £20) [Thanks to Paul Island]
Beer Token £2 coin [Andy M says that when they first appeared, a bear cost about £2]
Hampden Roar (Score) £20 [Thanks to Gary Robertson]
Cenny (century) £100 [Thanks to Gary Robertson]
Elsie Sixpence [from Coronation Streets Elsie Tanner - thanks to Carol]
Flag £5 [Thanks to Sparky James and Brian Spencer - Brian notes that £5 notes were at one time very large - this might explain the reference]
Garden Gate £8 [Thanks to Ian Crossley]
Taxi Driver Fiver - £5 {Thanks to David]
Joey Please look on the Questions page (link at the top of this page).
Shrapnel Refers to loose change [Thanks to Bruce Richardson]
Sheets General term for paper money [Thanks to Pete Orme]
Yard £1,000,000,000. [Thanks to George McLean who explains that each '000' is a foot, three feet equal one yard. Similarly, it could be a yard of yen or any other currency. Richard Stanton points out that yard is probably short for milliard, meaning 1 billion]
Dosh Any sort of money [Thanks to Lisl]
Double Nugget £2 coin [Thanks to Richard Sisson]
Bluey £5 [Because of the bills colour. Thanks to Stuart Bassett]
Charred £5 [He says that the ink on the notes often get burnt during manufacture. Thanks to Stuart Bassett]
Bertie £30 [Thanks to Stuart Bassett. Gerry Gavigan says this comes from the musical hall song "Burlington Bertie" (a tramp living in Burlington arcade in Knightsbridge) I'm Burlington Bertie I rise at ten thirty"]
Huckleberry Hound £1 [Thanks to Willie Mackay]
Bender Sixpence. I believe it got its name because real ones had a certain silver content and bending them was a way of proving this. It also led to the phrase 'going on a bender' which was a good night out drinking a whole sixpence worth! [Thanks to Peter Gazeley]
Grubby Hand £1,000 (grand) [Thanks to Jim Knight whose granddad says this expression was used in East London from Victorian times to the 1940's or 1950's.
Drinking Voucher Any denomination, the value determined by the colour - a "blue drinking voucher" would be £5 [Thanks to Nick]
Purple £20 [Thanks to Paul Brister]
Bucket of Sand £1,000 (grand) [Thanks to Andrew Tough]
Spot Each pound of a group - a ten spot would be £10, a twenty spot would be £20. [Thanks to John Lines who says this is commonly used - the spot indicates the decimal point]
Jake £5 [Thanks to Talktoi]
In the Green £25 [outer circle of the bull's eye - thanks to John Campbelton]
Heptagonal Bad Boy Another name for a twenty pence piece, used in pubs and bars for things like pool table and table football, though less so now since they usually are more expensive [Thanks to Daniel Dockery]
Spit Roast £25 [Thanks to Will who confusingly notes "because its two ayrtons and a lady"]
Stretch Tenner = 1stretch, 20 = 2 stretch, 50 = 5 stretch, etc. [Thanks to John who heard this on Commercial Road - the reference here is to prison terms]
Edge Pences 50p [Thanks to Paul Madgwick]
Half a Bar 50p [Thanks to Sig]
Sov or Sov's £1 [Short for sovereigns - Thanks to Ray Norgate]
Henry £10 [Russ says a tenner is called a Henry because of the picture on it and that an eighth of marijuana is called a henry because it costs a tenner. Matt completely disagrees with Russ - an eighth of marijuana is called a henry after Henry VIII, not because of the cost.]
Desmond £4 [Desmond Tutu (2 2) - thanks to Jeremy Adam]
String of Ponies Half a monkey (£250) - thanks to Wik
Emperor Ming Money in general [Rhymes with ka-ching (sound of a cash register). Thanks to Michelle Chiles]
Dartboard £2 coin [Because of the concentric circles in its design = Thanks to Rob Jones]
Super Nugget £2 [Origin unknown - Thanks to Martin Tilley]
Maggie £1 coin [From the eighties, of the then new gold-coloured one-pound coin, because, it was said, 'it's brassy, two-faced and thinks it's a sovereign' (the then Prime Minister, Margaret Thatcher, had a noticeable tendency to mimic some of the more regal characteristics of Her Majesty). Ivor Randle confirms: "As I recall, for a short while the then new pound coin was called a "Maggie" after Prime Minister of the time Margaret Thatcher, because it is "small and brassy, and thinks it's a sovereign"."]
Money that folds In general, all paper money. [Thanks to Tom Mathias]
Joes Thrupenny bit (3p) [Thanks to Toad]
Round Money Generally, coins [Thanks to Edward Williams]
Ten Bob Bit The new 50p coin [Thanks to Steve Bonnage]
Gorilla (Grilla) £1000 [According to Russell Holden, it's called this because it's two monkeys]
Brownie I understand that Ten Shillings (50p) - (Ten Bob) was a 'Brownie' because the old ten shilling note was coloured brown [Thanks to Geoff Richards-Bray]
Cherry £1 - In the '60s I was a craps dealer in London gambling clubs. Cockney 'cabbies' would play at our table, and call bets before the dice rolled. One night one of them handed me a 'fiver' with the words:" A 'Cherry' on the line mate!" I asked what he meant, and he quickly explained that he wanted £1.00 out of the fiver on the 'Win Line' 'Cherry' is short for 'Cherry Picker' which rhymes with 'nicker' which = £1.00! [Thanks to Tony Pirkis]
Groat four pence [There's lots of information at http://www.tclayton.demon.co.uk/fourd.html [Thanks to Nigel Lines]
Point £1 billion [Mark says this is used in the B of E and the European money markets - never really come up in my day to day]
Large £1000 [Thanks to Benjamin Rumble]
Rio £1000 [Thanks to Paul Page who says it comes from the Rio Grande River]
Pinky £50 [Thanks to Scott Hobson. If anyone know the origin of this please let me know.]
Tosheroon Half crown [Thanks to Sue Allen who read this in Sidney Day's London Born

....just to name a few!