Green’s Dictionary of Slang

wagtailed adj.

promiscuous.

1656		‘Basilius Musophilus’ Don Zara Del Fogoy 91: Always drinking, alwayes whoring, you spend your lives with wag-tayl’d Wives [...] Till your proud flesh make ye pocky.
1680		Winstanley Wit, mirth, and jollity 122: I know not which lead most unnatural lives, / Horn-headed husbands, or light wag-tayl’d wives.