regulator, n. — Green’s Dictionary of Slang

regulator n.

[? it stops men getting ‘over-heated’ or ref. to US gangs of Regulators, administrators of vigilante justice and who often adopted female dress for their raids]

the vagina.

[1752		N.Y. Gazette Revived 18 Dec. 2/2: We hear [...] that an odd Sect of People have lately appeared [...], who go under the Denomination of Regulators [...] who dress themselves in Women’s Cloaths, and painting their Faces, go in the Evening to the Houses of such as are reported to have beat their Wives; where one of them [...] seizes the Delinquent, while the rest [...] strip him, turn up his Posteriors, and flog him with Rods most severely].
1835		‘The Female Regulator’ in Secret Songster 26: She vow’d and protested she would bring it in; / She titled herself then the new regulator, / And stuck to the bargain as she had begun.
1890–1904		Farmer & Henley Sl. and Its Analogues.