/
ˈkɒnkeɪv/
adj.
 having an outline or surface that curves inwards like the interior of a circle or sphere. Compare with 
convex.
Derivative
- concavely adv.
  - concavity n. 
(pl. concavities)
. 
Etymology
ME: from L. concavus, from con- ‘together’ + cavus ‘hollow’.