Definition of periostracum
: a chitinous layer covering the exterior of the shell in many mollusks, being usually well developed in freshwater forms, and serving to protect the shell from corrosion
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 periostracum
New Latin, from peri- + Greek ostrakon shell — more at oyster
Seen and Heard
What made you want to look up periostracum? Please tell us where you read or heard it (including the quote, if possible).