Green’s Dictionary of Slang

very big, enormous, huge.

c.1440		Walsingham in Hone Year Bk (1832) 90: In delvinge he myghte [...] find a schwoppinge mallarde imprisoned in the sinke or sewere [OED].
1589		Nashe Countercuffe to Martin Junior in Works I (1883–4) 80: A filch-man in his hande, a swapping Ale-dagger at his back.
1615		T. Overbury New and Choise Characters n.p.: [A Puny-clarke] A Clarke of a swooping Dash, is as commendable as a Flanders horse of a large taile.
1624		Middleton Game at Chess IV ii: Ay, marry, sir, here’s swapping sins indeed.