CONCAVE

adj hollow; void of contents.

2. concave ·vt to make hollow or concave.

3. concave ·noun a hollow; an arched vault; a cavity; a recess.

4. concave ·noun a curved sheath or breasting for a revolving cylinder or roll.

5. concave ·adj hollow and curved or rounded; vaulted;

— said of the interior of a curved surface or line, as of the curve of the of the inner surface of an eggshell, in opposition to convex; as, a concave mirror; the concave arch of the sky.