Green’s Dictionary of Slang

1. a watch [it ‘tells’, i.e. predicts, the time].

1738

Swift Polite Conversation 49: col.: Pray, my Lord, what’s a Clock by your Oracle? lord sp.: Faith, I can’t tell; I think my Watch runs upon Wheels.

2. the vagina [the initial ‘O’ + the ‘o’ shape; the ‘mouth piece of the deity’].

1890–1904

Farmer & Henley Sl. and Its Analogues.