Green’s Dictionary of Slang

furbelow n.

[SE furbelow, an adornment to a dress or other garment, ult. f. falbala, trimming for women’s petticoats, scarves etc + pun on fur n. + SE below; the term begins as a ref. to a petticoat typically worn by a whore, then by metonymy to the woman herself, thence the pubic hair and/or vagina]

[18C–mid-19C] the female pubic hair; the vagina.