concave
US /ˈkɑːn.keɪv/
UK /ˈkɑːn.keɪv/
1.
having an outline or surface that curves inward like the interior of a circle or sphere
:
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The spoon has a concave shape.
•
The lens of the telescope is concave.
having an outline or surface that curves inward like the interior of a circle or sphere