Green’s Dictionary of Slang

1. (UK Und.) a sleep.

1846

Swell’s Night Guide 51: The nummy pet gammoned scrapping, stalled a prop in the mug, propped in return, and floored Fuzzle, who gammoned a downer.

2. (UK und.) a knock-out blow.

1906

D. Stewart Vultures of the City in Illus. Police News 29 Dec. 14/3: ‘I won’t queer your deal. I’ll give you a downer and then you must sham Abraham’.

3. (UK tramp) a bed.

1937–84

Partridge DSUE (1984) 337/1: —1935.