Originally Posted By: kah454
the Poop Deck on a sailing vessel was the rear deck above the cabin, from the french word for stern, la poupe.

...which in turn is from Latin, puppis, the stern. The largest constellation of the Greco-Roman period, Argo Navis (the ship of the Argonauts), covered such a vast swathe of sky that in the 18th Century the ship was broken up into its constituent parts: Vela, the sails; Carina, the keel; and Puppis, the poop deck/stern. Pyxis, the compass, is sometimes unofficially included in the wreckage.