Entry 1 sense Webster, 1913 Plano-concave · Pla·no-con·cave · IPA 01 a. Plane or flat on one side, and concave on the other; as, a plano-concave lens. See Lens. 1. Plane or flat on one side, and concave on the other; as, a plano-concave lens. See Lens. See: Lens