I would swear the OED is just messing with my head now.
"A one-piece garment providing protection for the whole body against the cold, wet, etc."
That's all well and good, until you look at the listed etymology:
"< a first element of uncertain origin + SUIT n.
The first element is perhaps < POOP n.2 (compare POOPY adj.2), on account either of the unpleasant smell of the suit when worn for a long time, or of the sound produced when excess air is expelled from it."