01 a. Concave on one side and convex on the other, as an eggshell or a crescent.
-
1.
Concave on one side and convex on the other, as an eggshell or a crescent.
-
2.
Specifically, having such a combination of concave and convex sides as makes the focal axis the shortest line between them. See Illust. under Lens.(Optics) See: Lens