Green’s Dictionary of Slang

1. an act of sexual intercourse [note earlier gallop v.].

c.1900		A. Cairene Sixfold Sensuality 75: Adolph then mounted the pretty through bred, who was lying on her back eagerly waiting for a gallop.
1974		‘P.B. Yuill’ Hazell Plays Solomon (1976) 36: That morning’s little gallop was helping me recapture some of my winning ways.

2. (US) a dance.

1941

J. Archibald ‘Alibi Bye’ in Popular Detective June 🌐 The boys are gettin’ up dough to throw a gallop in Cooley’s Hall on East Thirteenth Street.

3. (Aus.) a fight.

1959

D. Niland Gold in the Streets (1966) 107: ‘Let’s have another gallop.’ Danno fought aggressively.

4. (Aus.) in pl., horseracing.

2013

T. Peacock More You Bet 15: ‘The horses’ (which were and are also known as ‘the gallops’, or ‘the nags’, or ‘the neddies’ or the ‘gee-gees’).