Douglas Harper's Etymology Dictionary
"sex with a woman; woman regarded as a sex object; female genitalia," c.1910, of uncertain origin, probably via New Orleans Creole, from French putain "prostitute," from Old French pute "whore" (cognate with Spanish and Provençal puta), probably from fem. of Vulgar Latin *puttus "girl" (source of Old Italian putta "girl"), from Latin putus (originally "pure, bright, splendid").\n
\nBut also possibly from or influenced by Old French put, from Latin putidus "stinking" on notion of the "foulness" of harlotry [Buck], or for more literal reasons (among the 16c.-17c. slang terms for "whore" in English were polecat, which might also be a pun, and fling-stink). Shortened form poon is recorded from 1969.
Wiktionary
n. 1 (context US colloquial vulgar English) Female genitalia; the vulva or vagina. 2 (context US slang vulgar uncountable English) sexual intercourse with a woman.
Usage examples of "poontang".
He pulled up alongside a life raft full of Refus one day, looking for some poontang, and he was dead before he knew it.
He sat back and scratched his purple hair, all thoughts of poontang gone.
The poontang just a fringe benefit, make the asshole members feel good.
Then it occurred to him if he was queer he was certainly banging one hell of a nice poontang about ten times a night.
Paolo said the squareheads sailed west looking for beer, and Dad said the dagos sailed west looking for poontang.
Cayuses and fillies and remudas and geldings and poontangs and chaps and spurs that jingle-jangle-jingle.