keyhole, n. — Green’s Dictionary of Slang

keyhole n.

the vagina.

1607		Dekker & Webster Westward Hoe V i: Puh, good maister Lynstocke, Ile not stand by whilst you giue Fire at your Key-holes.
1684		Rochester (attrib.) Sodom in Ashbee Centuria Librorum Asconditorum (1879) 339: V i: They’re apt to utter their complaints before / They come to find the keyhole of the door.
1713		A Dreadful Fire 5: Here’s Peter’s Key, and as you Sit, / Let’s try how Peter’s Key will fit / Thy Key-hole.
1924		Virginia Liston [song title] You’ve Got The Right Key, But The Wrong Keyhole.
1981		McKee & Chisenhall Beale Black & Blue 116: Some of his Memphis friends were afraid he’d tell the one about why he had broken off a long-standing relationship with a woman friend: ‘My key,’ he would say impishly, ‘don’t fit her keyhole no more.’.

keyhole-whistler (n.) (also keyhole-whisperer) [those inside the adjacent house hear whispering/whistling through the keyhole]

1. one who sleeps in barns or outhouses, thus a tramp or vagrant.

1859, 1860		Hotten Dict. of Modern Sl. etc.
1861		(con. 1840s–50s) H. Mayhew London Labour and London Poor I 311/1: ‘Keyhole whistlers,’ the skipper-birds are sometimes called, but they’re regular travellers.
1891		F.W. Carew Autobiog. of a Gipsey 413: A rough lot they were [...] reg’lar keyhole whistlers the lot of ’em, skipperin’ it for choice when they’d got the price of a doss about ’em.

2. (US Und.) a criminal in hiding.

1935

A.J. Pollock Und. Speaks.