Crossword puzzle clue "concave object of reflection"

a piece of transparent matter with one or both surfaces curved to cause regular convergence or divergence of rays passing through it

having an outline or surface curved like the exterior of a circle or sphere

a valley

DENT, to make a depression in

DISH, to put into a concave vessel

(French) a sword similar to the foil but with a larger guard and a heavier blade of triangular cross section

a plastic disk several inches in diameter sailed between players by a flip of the wrist