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)]

[early 19C+] (orig. Anglo-Ind.) a drink, esp. of brandy and soda.

In compounds

peg-house (n.)

[1920s–30s] a public house.

In phrases

go a peg lower (v.)

[19C] to drink heavily.

king’s peg (n.)

[late 19C+] a champagne cocktail, champagne mixed with brandy.

put in the peg (v.) (also put on the peg) [late 19C–1920s] (Aus.)

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

2. to cut off someone’s credit.