Green’s Dictionary of Slang

broadside n.

an act of sexual intercourse, an ejaculation.

[UK]T. Bropwn et al. [trans.] Comical works of Monsr. Scarron 26: Tell me, Bully Rock, art thou still strong and Iusty? Are the Bona Roba’s kind, and will they venture a Broad-side with one?