Green’s Dictionary of Slang

fat, large-buttocked; also of objects, large.

1705–07		N. Ward Hudibras Redivivus I:10 11: Some fat-ars’d Sows and lusty Loobies / Were got on Galloways and Hobbies.
1749		Fielding Tom Jones (1959) 564: That fat-a—se b—, my Lady Bellaston.
1837		‘He’ll No More Grind Again’ in Ri-tum Ti-tum Songster 29: A kid, he bolted from his home [...] With red-haired Moll, the fat a--e mot.
1870		Cythera’s Hymnal 33: My charming fat-arsed Valentine.
1888–94		‘Walter’ My Secret Life (1966) III 524: I [...] admired even at one time a fat-arsed middle-aged woman who sold us bull’s eyes.
1970		C. Brown Down All the Days 111: You big fat-arsed coward!
2001		N. Barlay Hooky Gear 27: Boss bein the fat-arse ponce with brown socks.
2001		A. Sillitoe Birthday 150: The drivers no doubt fed up with seeing the same fat-arsed pantechnicon.
2012		J.J. DeCeglie ‘Death Cannot Be Delegated’ in Crime Factory: Hard Labour [ebook] His fatarse paunch sitting on the felt of the table banking ball after ball.
2024		J. Meades Empty Wigs (t/s) 116: Vee-pee-ell - that’s my only message for the fat-arsed mouthy one from The Human Flotsam Hub.