a curve; bend.

a curving part or recess.

Anatomy .

any of various cavities, recesses, or passages, as a hollow in a bone, or a reservoir or channel for venous blood.

one of the hollow cavities in the skull connecting with the nasal cavities.

an expanded area in a canal or tube.

Pathology . a narrow passage leading to an abscess or the like.

Botany . a small, rounded depression between two projecting lobes, as of a leaf.

noun

antrum , cavity , channel , depressing , hollow , opening , pocket , recess