Green’s Dictionary of Slang

1. (Irish) assistance, help [image of giving someone a leg over a stile or gate].

1997

Share Slanguage.

2. (orig. milit.) sexual intercourse; thus give/have a bit of legover, to have sexual intercourse [back form. f. get one’s leg over under leg n.].

1975		A. Bleasdale Scully 18: She’s a bit free with the old ‘leg over’ when she’s had a few.
1989		J. Morton Lowspeak.
2002		J. Cameron Hell on Hoe Street 123: She sounded like ready for a legover.
2010		K. Richards Life 222: Stash had the bullshit credentials of the period [...] all basically employed in the service of leg-over.
2014		me-stepmums-too-fuckin-hot-mate at www.fakku.net 🌐 Fuuuuuck me, Masumi-san. Get a leg over.