Concavo-convex /(?)/

Con·ca·vo-con·vex

Concavo-convex

a.
  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)