How did the British pound come to be known as a 'nicker'?

The most common slang term in Britain these days for a pound is quid, a term which was once used also of the guinea. It is always used in the singular, so one speaks of 'ten quid' or 'fifty quid', never of 'quids', except in some set expressions such as quids in, meaning 'in {luck;} well off for money'. It may derive from the Latin quid 'what?' or from some association with the quid of chewing tobacco, which itself is just a variant of cud. This is pretty widely used throughout the country, but a rather older term, which has become less common recently and has much stronger London associations, is nicker. This dates from early this century (it explains that terrible old joke: 'Why can't a one-legged woman change a pound note? Because she's only got half a (k)nicker!') and which nobody seems to know the origin of. https://www.learnenglish.de/slang/moneyslang.html

Nothing I have researched (including a dictionary of slang) gives an origin for the word nicker. The following extracts from a website might be of use.

It is difficult to trace the etymology of slang. Often, by the time a word is sufficiently well-recognized to merit investigation, its true origins have been lost to living memory and become layered with folk etymologies which prove impossible to dislodge. In these cases, we can do little more than make some informed speculations.

'Nick' has a wide variety of meanings based on cheating, snatching, and stealing.

http://www-personal.umich.edu/~jlawler/ask/nixer.html

Maybe, a one pound note was viewed as an item of currency worth nicking and became known as a nicker.

From the Oxford English Dictionary:

Brit. slang.

Plural unchanged, -s. [Origin unknown.
Perhaps originally Horse Racing slang.]

One pound sterling; a sovereign (obs.).

1871 H. J. BYRON Cyril's Success (new ed.) III. 45, I shall only be too delighted... That's a nicker for Treherne.

1910 Sessions Papers 1 June 128, I suppose this has cost you a couple of ‘nickers’.

1960 D. LESSING In Pursuit of Eng. ii. 66 It's a little matter. A hundred nicker. And it'd double itself in a year.

2000 J. CAUGHIE Television Drama iv. 116 Don't go far when you're used to a hundred nicker in yer pocket.

The concept nicker as one who steals is given by the OED as a separate definition not related to the money one. By the way, 'quid' is older (first recorded use 1661), again, from the OED:

colloq. (chiefly Brit., Austral., and N.Z.).


Plural unchanged, -s. Forms: 16 quidd, 16- quid. [Origin uncertain; perhaps < classical Latin quid what (see QUID n.1), reinterpreted within English to refer to (monetary) means or wherewithal.
It has also been suggested that this is the same word as QUID n.3 [wad of tobacco], but that is first attested later.
It has been suggested that the following shows an earlier example, but this seems unlikely:
?a1558 in Kent Rec. (Kent Archaeol. Soc.) (1999) 3 II. 91 Item resayved (?)for vj bs. of loges pris x quid the lode.]

1. a. Originally: a sovereign; a guinea. Later: one pound sterling; (formerly also) one Australian pound.
Now usu. with unchanged plural following a cardinal numeral: cf. etymological note at POUND n.1

1661 P. ARETINE Strange Newes from Bartholomew-Fair 5 The fool lost his purse, but how he knew not; for the reckoning being suddainly brought in, his Quids were vanisht. 1688 T. SHADWELL Squire of Alsatia III. i. 42 Let me Equip you with a Quid. 1763 Blessings of P****, & Sc. Excise 23 I'm to have two quids; and little enough too. 1796 Mod. Gulliver 165 The twenty last are worth full forty quid. 1834 W. H. AINSWORTH Rookwood III. III. xiii. 166 One quid, two coach wheels. 1883 W. BESANT All in Garden Fair II. x, It isn't two quid a week that will keep a young gentleman of your powers. 1907 G. B. SHAW Major Barbara II. 241, I ad two quid saved agen the frost; an Ive a pahnd of it left. 1929 W. P. RIDGE Affect. Regards 71 Milton received only ten quid for the first edition of ‘Paradise Lost’. 1968 K. WEATHERLY Roo Shooter 74, I was thinking of moving on a bit but there are still enough here to make a few quid. 1993 Classic CD Oct. 66/3 No-one is going to shell out 40 quid for them.

b. quids in: in luck or profit; well off for money.
1919 Athenæum 1 Aug. 695/2 Quid's in, for a stroke of good fortune. 1928 ‘N. SHUTE’ So Disdained v. 206 Then when they come I'll be quids in, anyway enough to get my fingers on the plates with any luck. 1969 J. N. CHANCE Abel Coincidence x. 187 If you know about people and they know nothing about you, you're quids in at the starting grid. 1994 Chat 5 Feb. 24/2 Three lucky Chat readers will find themselves quids in with this great cash competition.

c. Austral. and N.Z. the full quid: in full possession of one's mental faculties; bright, intelligent. Freq. in negative constructions.
1944 Austral. New Writing 36 He'll back down; I said he wasn't the full quid, just a skite. 1960 N. HILLIARD Maori Girl III. vi. 213 Not that she was simple in the sense that she was short of the full quid. 1975 Sydney Morning Herald 5 July 9 It's perfectly clear that not all members of our community are the full quid. 2006 Weekend Austral. (Nexis) 20 May 30 Pauly accosts a local in the town who does not look the full quid..and who affords the opportunity for jokes about in-breeding and village idiots.

2. As a mass noun: money, cash. Usu. in pl. (with sing. concord). rare{em} 0.
1699 B. E. New Dict. Canting Crew, Quidds, money. 1881 A. TRUMBLE Slang Dict. (at cited word), Quids, cash. 1937 E. PARTRIDGE Dict. Slang at Quid, Money, or rather cash, in general.

Slightly dated sounding now - and beware, the plural of nicker is nicker. Visitors are best not to use this term. Knickers are always plural even when there's only one pair, and are not usually acceptable as currency. (Depends on with whom you are doing business...) Snickers is a sweet bar that Baloo last bought when it was called Marathon. (Mars probably haven't noticed, but there are a few of us not buying them.)