Green’s Dictionary of Slang

drop n.4

[lit./fig. uses of SE drop, a portion]

1. [mid-18C+] (also drop of something, …of the necessary, ...of the other) a drink; often as drop of the creature under creature, the n.

2. [1960s] (Aus.) a young woman.

3. [1960s] (Aus.) a good thing.

In phrases

drop in one’s eye (n.)

see separate entry.

have the big drop on (v.)

[1960s] to be drunk.