ple·si·o·saur (plēsē-ə-sôr, plēzē-)
n. pl. ple·si·o·saurs
Any of various extinct marine reptiles of the group Plesiosauria of the Mesozoic Era, having paddlelike limbs, a short tail, and sometimes a very long neck.
[New Latin Plēsiosaurus, type genus : Greek plēsios, near to; see pel-5 in the Appendix of Indo-European roots + Greek sauros, lizard.]
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2018 by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
The American Heritage Dictionary Blog
Check out our blog, updated regularly, for new words and revised definitions, interesting images from the 5th edition, discussions of usage, and more.