Green’s Dictionary of Slang

1. (also whump) a heavy, low sound.

1926		Blackwood’s Mag. May 595/2: Ever think of Piccadilly in the evening, and the ‘whomp’ of an orchestra starting up in some theatre?
1961		H. Ellison Rockabilly (1963) 130: It was gutty, almost burley bump-&-grind treatment with every whump!
1972		B. Rodgers Queens’ Vernacular 213: whomp (inter!) onomatopoetic sound to emphasize force, speed or excessive pressure and length.

2. a spree.

1957

H.S. Thompson letter 5 Aug. in Proud Highway (1997) 61: I returned from a three-day whomp in New Orleans.

3. a heavy blow.

1970

J.H. Gray Boy from Winnipeg 145: We got some special whomps just in case we had sneaked anything .