Green’s Dictionary of Slang

poop n.1

[SE poop, the stern or highest stern deck of a boat]

1. [late 16C–17C] the vagina.

2. [17C–early 18C] the ‘dickey’ or rear seat of a coach.

3. [mid-17C+] the buttocks, the anus.

In compounds

poop-noddy (n.) (also pup noddy) [SE nod, to bob up and down]

[16C] sexual intercourse.

In phrases

get it up the poop (v.)

[1960s] to suffer; to be exploited.