Green’s Dictionary of Slang

peg n.4

[? each drink was seen as a ‘peg [i.e. nail] in one’s coffin’; but note 17C SE peg, ‘one of a set of pins fixed at intervals in a drinking vessel as marks to measure the quantity which each drinker was to drink’ (OED)]

(orig. Anglo-Ind.) a drink, esp. of brandy and soda.

[UK]Egan Life in London (1869) 210: [...] to chaff with the flash Mollishers; and in being home to a ‘peg’ in all their various sprees and rambles .
[US]W. Otter Hist. of My Own Times (1995) 66: We kept the pegs moving [during a spree] for two nights, and the way it wound up was just nobody’s business.
R.F. Burton Scinde 289: Many a man supports his mind through half a summer by means of a meagre pun, or some bare bit of slang, as ‘fin,’ for old fellow, and ‘peg,’ signifying a glass of pale brandy and soda-water.
[UK]Hotten Dict. of Modern Sl. etc. (2nd edn).
G. F. Atkinson Curry & Rice (3 edn) n.p.: [E]ventually do we tear ourselves away, fling ourselves horizontally on the cushions of our vehicle, light our cheroot, quaff our last ‘peg,’ [...] the team moves on, and a parting cheer vibrates in the air as we pass through the compound-gate.
[UK]G.A. Sala in Belgravia Apr. n.p.: Ensign Plume of the 200th Foot, at present languishing obscure at ‘Gib’ and taking too many pegs of brandy and soda when on guard [F&H].
[UK]Westmorland Gaz. 28 Jan. 6/5: Their demoralization is extraordinarily rapid when once they have taken to ‘pegs’ between meals .
[UK]Daily News 7 May in Ware (1909) 227/1: Abdullah Bey would smash a brandy peg with any one of us, and on the present occasion quaffed his laager beer like a stolid old Dutchman.
[UK]Kipling ‘The Big Drunk Draf’’ Soldiers Three (1907) 30: [of whisky] He helped himself to a fresh peg.
[Aus]Dead Bird (Sydney) 16 Aug. 2/4: I am much addicted to swearing English oaths, drinking dam lots of pegs and other ramifications.
E. Cuthell In Tent and Bungalow 19: We had each, Blake and I, a stiff peg from Bob’s soda-water basket.
[UK]J. Conrad Lord Jim 16: I could drink liquid fire against your whisky peg for peg, b’gosh, and keep as cool as a cucumber.
J. Ayscough Mr Beke of Blacks 235: At this moment, however, Mr. Fane is sipping a peg in the ante-room of the mess, and talking war sapiently.
[Aus]Bulletin (Sydney) 1 Dec. 40/4: My Love is as bald as an egg, / And red as a beet is his nose; / For years he has taken his ‘peg’; / Immense bills for whisky he owes.
[UK]‘Sax Rohmer’ Dope 131: ‘You’re right, old bird!’ said Jim, pouring out a stiff peg of the spirit.
[UK]Galsworthy White Monkey 323: Have a peg, sir? I’ve got brandy here.
[UK]D.L. Sayers Have His Carcase 184: He poured himself out a stiff peg.
[Aus]X. Herbert Capricornia (1939) 26: [He] got out a bottle that was roughly labelled Henn’s Ambrosia, and drank a peg.
[US]S. Longstreet Decade 194: A peg of whisky.

In compounds

peg-house (n.)

a public house.

[UK]Partridge DSUE (1984) 866: [...] from ca. 1920.

In phrases

go a peg lower (v.)

to drink heavily.

[[UK]Chester Courant 4 May 4/4: The meaning of ‘A Peg Too Low’ — the Peg tankard, a species of wassail bowl [...] which was divided by pegs to ascertain the quantity each person drank].
[UK]Farmer & Henley Sl. and Its Analogues.
king’s peg (n.)

a champagne cocktail, champagne mixed with brandy.

[Aus]Bulletin (Sydney) 8 Dec. 14/2: I’ll take payment in kind – one page – any one page – for a case of fizz – the genuine article – and three bottles of three-star. The other fit’s coming on, and I’d like to taste King’s Peg again.
put in the peg (v.) (also put on the peg)(Aus.)

1. to stop doing something, esp. to stop drinking.

[UK]Partridge DSUE (8th edn) 866/1: C.19–early 20.

2. to cut off someone’s credit.

[UK]Partridge DSUE (8th edn) 866/1: late C.19–20.