Green’s Dictionary of Slang

1. (UK juv., also whap, wop) a blow, a hit; thus a beating, a caning.

1818		W. Perry London Guide xii: whop a blow or slap.
1831		Quizzical Gaz. 27 Aug. 7/2: Joe’s patience lost, he gives her such a vop.
1837		R. Barham ‘The Bagman’s Dog’ in Ingoldsby Legends (1840) 333: Extremely annoy’d by the ‘tarnation whop,’ as it’s call’d in Kentuck, on his head and its opposite.
1862		Capt. Clutterbuck’s Champagne 184: What a whop!
1866		Cornish Teleg/ 5 Dec. 2: I advised her to change et [...] which I got another wop in the mouth .
1888		S.O. Addy Sheffield Gloss. 275: Wap or Wop, a blow.
1905		H.G. Wells Kipps (1952) 70: I came rather a whop.
1906		Queenslander (Brisbane) 14 Apr. 44/4: The rough rider went skyward [...] and descended with a vicious ‘whop’ on the head.
1923		Kipling ‘The Janeites’ in Debits and Credits (1926) 150: ‘It was a wop too: ’ead-on — like this!’ And he slapped his tactful little forehead to show what a knock it had been.
1961		‘Frank Richards’ Billy Bunter at Butlins 34: ‘That means whops!’ said Johnny Bull.
1967		P. Thomas Down These Mean Streets (1970) 4: The second whap of the belt brought words of pain to my lips.

2. (US Und.) a sentence of 15–30 days.

1904		‘Number 1500’ Life In Sing Sing 267: He calls out his remaining time [...] or forms the words with voiceless mouth so that they may be read on his lips, ‘two and a whop,’ or ‘one and a whisper,’ as the case may be.
1919		NY Tribune 8 June 7/5: ‘Whop’ [a sentence of] over fifteen days but less than a month.
1949		Monteleone Criminal Sl. (rev. edn).

3. a fine example.

1929

M. Levin Reporter 333: It really makes a whop of a story.

4. (US black campus, also whupp) a hangover.

1947

M.H. Boulware Jive and Sl.

5. (US) a go, a time.

1971		R.D. Pharr S.R.O. (1998) 474: ‘That’s what I’m gonna be [...] Two bags at a whop, four times a day’.
1986		Chapman NDAS.
1997		L. Pettiway Workin’ It 244: No negociation ’cause each cap is worth five or ten dollars a whop.