Green’s Dictionary of Slang

nip n.6

[SE nip, a portion of alcohol]

SE in slang uses

In compounds

nip joint (n.) [joint n. (3b)]

[1970s+] (US) an illegal drinking establishment where drink is sold in nips or small (orig. half-pint) measures.

Nip Shop (n.) (also nyp shop)

[late 18C–early 19C] the Peacock Tavern in Gray’s Inn Lane, London, where Burton ale was sold in nips or half-pint measures.

In phrases

freshen the nip (v.)

[mid-19C] to have a drink.