[con.cave] adj [ME, fr. MF, fr. L concavus, fr. com- + cavus hollow--more at cave] (15c) 1: hollowed or rounded inward like the inside of a bowl
2: arched in: curving in--used of the side of a curve or surface on which neighboring normals to the curve or surface converge and on which lies the chord joining two neighboring points of the curve or surface
[2]con.cave n (1552): a concave line or surface