Green’s Dictionary of Slang

pubic hair, usu. female; cit. c.1660 is part of a lengthy hunting-based double entendre; ‘beagles’ are the testicles.

c.1660		‘I Dreamed My Love’ in Furnivall & Hales Bishop Percy’s Folio Manuscript of Loose and Humorous Songs (1868) 102: Methought her belly was a hill / much like a mount of pleasure, / under whose height there growes a well; / the depth no man can measure. / about the ple[a]sant mountaines topp / there growes a lovely thickett, / wherein 2 beagles trambled. / & raised a lively prickett.
1680		M. Stevenson Wits Paraphras’d 131: Close by my Thighs, a gloomy thicket / Lies languishing for thee, my Pricket.
[1748–49		Cleland Memoirs of a Woman of Pleasure (1985) 63: He drew up his shirt, and bared all his hairy thighs, and stiff staring truncheon, red-topt, and rooted into a thicket of curls].
1888–94		‘Walter’ My Secret Life (1966) X 1984: I saw the puffy motte and delicate notch, with a slight nut-brown thicket about it.
1982		N. Keesing Lily on the Dustbin 40: Feminine pubic hair is a ‘thicket.’.