Green’s Dictionary of Slang

1. to seduce, to pick up and, poss., to go to bed with.

1959

W. Hall Long and the Short and the Tall Act II: That’s better than you cop on from those Tokyo geisha fillies.

2. to grab hold of.

1938		F.D. Sharpe Sharpe of the Flying Squad 330: cop: To receive. (‘I copped on a quid’).
1958		(con. 1940s) B. Behan Borstal Boy 314: Cop on, Pat.
1959		W. Hall Long and the Short and the Tall Act II: So why did you cop on for the tape in the first place?
1962		R. Cook Crust on its Uppers 20: Copped on to this job in London.
1996		J. Murphy A Picture of Paradise in McGuinness Dazzling Dark (1996) Act I: Would you cop on!

3. get a grip on oneself.

1972		(con. 1940s) N. Conway Bloods 94: Shut up and cop yourself on.
1988		R. Doyle Commitments 12: Ah, cop on, said Jimmy. – I was only messin’.
1996		(con. 1970) G. Moxley Danti-Dan in McGuinness Dazzling Dark (1996) I iv: Cop yourself on, will you.
2004		P. Howard PS, I Scored the Bridesmaids 84: It was me who basically got her to cop onto herself.

4. see cop v. (3d)