marine cephalopod, c. 1600, from Latin nautilus, in Pliny a kind of marine snail (including also squid, cuttlefish, polyps, etc.), from Greek nautilos "paper nautilus," literally "sailor," from nautes "sailor," from naus "ship" (from PIE root *nau- "boat"). From Aristotle into the 19c., the nautilus was believed to use its webbed arms to sail along the surface of the sea.
For thus to man the voice of nature spake,
Go, from the creatures thy instruction take,
Learn of the little Nautilus to sail,
Spread the thin oar, and catch the driving gale