Green’s Dictionary of Slang

1. a scheme, usu. criminal, an example of criminal activity.

1923		Smith’s Wkly (Sydney) 11 Aug. 15/4: Stringhalt prats herself in with him. When she had him ripe for the lumber, we said so long.
1956		‘Charles Raven’ Und. Nights 155: It wasn’t long before he came back with a lumber which he’d picked up from Barney Newbiggin and Cyril Toone in a cafe. A team had screwed a furrier’s in the East End and the gear was in the flat of one of their associates.

2. sexual play, petting.

1962		F. Norman Guntz 195: We were having a little lumber in a corner.
1966		P. Willmott Adolescent Boys of East London (1969) 55: They ‘titted a girl up’ or ‘had a bit of lumber’, ‘went up her skirt’.
1995		Sun. Trib. (Dublin) 9 July n.p.: In the weeks before, we stayed out late, kissed girls (lumbered, we said then, and it describes our technique perfectly) [BS].

3. (mainly Scot.) a prospective sexual partner, a casual pick-up.

1973		(con. mid-1960s) J. Patrick Glasgow Gang Observed 56: Yir lumber’s a cow.
1989		J. Morton Lowspeak 95: Lumber – a girl taken home after a dance.

4. violence, a fight.

2000

N. Griffiths Grits 449: I am a fuckin coward, ah yeh, av got no qualms abaht admittin that; first sign av lumba an am away like tha fucking clappers.