Definition of plesiosaurus
1 capitalized : a genus of marine reptiles (suborder Plesiosauria) of the Mesozoic of Europe and North America having a very long neck, a small head, and all four limbs developed as paddles for swimming
2 plural plesiosauri \-ȯˌrī\ : any reptile of the genus Plesiosaurus
Love words? You must — there are over 200,000 words in our free online dictionary, but you are looking for one that’s only in the Merriam-Webster Unabridged Dictionary.
Join MWU now and get access to America’s largest dictionary, with:
- 300,000 words that aren't in our free dictionary
- Expanded definitions, etymologies, and usage notes
- Advanced search features
- Ad free!
Origin and Etymology of plesiosaurus
New Latin, from plesi- + -saurus
Seen and Heard
What made you want to look up plesiosaurus? Please tell us where you read or heard it (including the quote, if possible).