plesiosaur

UK: /ˈpliːsɪəˌsɔː/ US: (plē′sē ə sôr′)

WordReference Random House Unabridged Dictionary of American English © 2026

ple•si•o•saur  (plē′sē ə sôr′), n. 

1. Paleontology any marine reptile of the extinct genus Plesiosaurus, from the Jurassic and Cretaceous periods, having a small head, a long neck, four paddlelike limbs, and a short tail.

• Neo-Latin Plesiosaurus (1821), equivalent. to Greek plēsí(os) near, close to + -o- -o- + saûros -saur; origin, originally so named because of its conjectured nearness to modern reptiles, relative to the ichthyosaurs

ple′si•o•sau′roid, adj. 

Collins Concise English Dictionary © HarperCollins Publishers::

plesiosaur / ˈpliːsɪəˌsɔː/ noun

1. any of various extinct marine reptiles of the order Sauropterygia, esp any of the suborder Plesiosauria, of Jurassic and Cretaceous times, having a long neck, short tail, and paddle-like limbs
   See also ichthyosaur
   Compare dinosaur, pterosaur

Etymology: 19th Century: from New Latin plēsiosaurus, from Greek plēsios near + sauros a lizard