1. A depression or cavity formed by a bending or curving.
2. Anatomy.
   1. A dilated channel or receptacle containing chiefly venous blood.
   2. Any of various air-filled cavities in the bones of the skull, especially one communicating with the nostrils.
3. Pathology. A fistula leading from a pus-filled cavity.
4. Botany. A recess or indentation between lobes of a leaf or corolla.

[Middle English, hollow in the body, from Medieval Latin, from Latin, curve, hollow.]

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.