Green’s Dictionary of Slang

a silent breaking of wind.

1568		A. de Guevara [trans.] The dial of princes n.p.: [O]ftentimes some holsome fleshe corrupteth in an euill vessel, and good wine sometime fauoreth of the foist.
1593		Nashe Four Letters Confuted in Works II (1883–4) 204: I am afraide your Doctors fart will fall out to be a fatall foyst to your breeches.
1605		Chapman & Jonson Eastward Ho! IV ii: Marry, fyst o your Ruidess. I thought as much.
a.1661		‘The Re-resurrection of the Rump’ in Rump Poems and Songs (1662) II 3: Why a Fart hath a tongue, and a Fyest hath none.
c.1698		B.E. Dict. Canting Crew n.p.: Foyst . . .a close strong Stink, without Noise or Report.
1725		New Canting Dict. [as cit. c.1698].