Green’s Dictionary of Slang

(US) a welcome or unwelcome fondling or handling of the breasts, buttocks or genitals.

1772		Bridges Burlesque Homer (3rd edn) 431: He saw [...] some ruddy country lass / That took his eye so much, he was / Contriving how to get a grope-a, / Or bull her, as he did europa.
1797		Bridges Burlesque Homer (4th edn) II 250: [as cit. 1772].
1888–94		‘Walter’ My Secret Life (1966) I 130: Couples used to come for a grope, a frig, or even for a fuck.
c.1900		‘Ramrod’ Nocturnal Meeting 11: Encouraged by this very loose conduct on the young lady’s part I was just about to have a grope.
1965		L. Dunne Goodbye to The Hill (1966) 71: There was always a load of mots who were on the look-out for a good neck and a grope.
1971		F.J. Hardy Outcasts of Foolgarah (1975) 22: He went the grope up the fleshy thigh for a bit of stink finger. [Ibid.] 197: Who do you think made up the story about Sneed coming the old grope on Liza Minnelli?
1979		J. Morrow Confessions of Proinsias O’Toole 4: He [...] had a quick grope at Stephanie’s bum whilst nibbling her cheek.
1987		(con. 1920s) L. Redmond Emerald Square 95: Some grown up ‘jazzers’ [...] who, all blemmed up, were heading for the Fountain Picture House in James Street for a session of cinema and sex and an exercise in ‘grope therapy’.
1999		Indep. Rev. 26 Aug. 7: A gang grope with the subject’s right hand running amok through your underwear.
2003		K. Cage Gayle 73/2: grope v. fondle genitals through clothing (Poor old queen, all he gets is a quick grope before they Bella him!).