concavo-concave

adj. (concave on both side—used esp.of a lens) उभयअंतर्वक ,adj. (of a lens—having the concave side of greater curvature than the convex side; concave on one side and convex on the other) अंतर्बहिर्वक्र (अंतर्वक्र बहिर्वक्र)