periostracum Hear it!

periostracum definition

peri·os·tra·cum (per′ē äs′trə kəm)

noun pl. periostraca -·ca (-kə)

a horny covering, secreted as the outermost layer of most mollusk shells, that protects the underlying shell from erosion

Etymology: ModL < Gr peri-, around (see peri-) + ostrakon, a shell: see ostracize

Webster's New World College Dictionary Copyright © 2009 by Wiley Publishing, Inc., Cleveland, Ohio.
Used by arrangement with John Wiley & Sons, Inc.

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