1. The act or process of making or becoming thick.
2. Material used to thicken: stir in a thickening of flour and water.
3. A thickened part.

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.