Green’s Dictionary of Slang

the vagina.

c.1564		Buckley ‘Oxford Libell’ in Arundel Harrington Ms. I 224: Not far from thence there was a warde had speciall grace against a thruste with buckler bente for softe and harde and foyne there at myght he that lust.
1593		Tell-Trothes New-Yeares Gift (1876) 30: Ioane, communis omnibus, that could play at bucklers so soone as she was past her cradell. Oh she is a tall peece of flesh, and will stand to her tackling so stoutly.
1608		Machin & Markham Dumbe Knight III i: Theirs nothing but beautie, vse and old age that puts women of my ranck out of request, and yer like old bucklers, though fewe of your gallant cauileres will weare vs, yet many of your stale Ruffins will imploy vs.