Green’s Dictionary of Slang

a fat woman.

1578		Lyly Euphues and his England (1916) 103: If she be well set then call her a boss, if slender a hazel twig.
c.1587		Marlowe Tamburlaine Pt I III iii: zab.: Base concubine, must thou be plac’d by me, That am an Empresse of the mighty Turke? zen.: Disdainful Turkess and unreverend Boss!
1611		R. Cotgrave Dict. of Fr. and Eng. Tongues n.p.: A fat boss, Femme bien grasse et grosse; une coche.