Merkin (first use, according to the OED, 1617) is reported to be a pubic wig, worn by prostitutes after shaving their genitalia to eliminate lice or to disguise the marks of syphilis. A similar, though anachronistic, claim not made in OED is that merkins were worn for nude stage appearances. The narrator of Vladimir Nabokov's Lolita (1955) recalls "Although I told myself I was looking merely for a soothing presence, a glorified pot-au-feu, an animated merkin, what really attracted me to Valeri was the imitation she gave of a little girl."
en.wikipedia.org/wiki/Merkin