1. The inner lining of the fourth stomach of calves and other young ruminants.
2. A dried extract made from the stomach lining of a ruminant, used in cheesemaking to curdle milk.
3. See rennin.

[Middle English, probably from Old English *rynet.]

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.