Choad/Chode--origin?

[Sam Clements]

Lighter in RHDAS suggests that "origin unknown."

He cites "choad" from 1968 to mean "penis."
He cite "choan" to mean copulation, from 1974(although some cites were from
students who remembered the word from the 1960's).

A poster over at the Straight Dope Message Board, who I accept as a
knowledgeable individual on many non-English words suggests that it come
from "....the Hindustani word cod (pronounced chode) meaning 'fuck'.

(Warning: this is a very rude word in Hindustani, so do not practice using
it around your Indian friends unless they are, you know, really really good
friends.)"

http://boards.straightdope.com/sdmb/showthread.php?s=&threadid=101902