1. An old shellfish or turtle with a growth of algae on its back.
2. An old, large, or sluggish fish.
3. An extremely conservative or old-fashioned person.

The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company. All rights reserved.