"Lloyd E. Sponenburgh" writes:

Nope, it has a quite definite etymology, but a rather exotic one.

The story I've heard is that it refers (in some way I could never
figure) to cannonballs and powder monkeys on Naval ships.

I don't believe this though ... it has a certain aura of
implausibility to it, and just *feels* like a back-formation.
I've certainly never seen convinving evidence of it.