A polygon is concave if it has angles of greater than 180 degrees between consecutive sides, eg a dart or arrow-head shaped polygon is concave, but a pentagram is not, because although it is not convex, all of its five angles are less than 180 degrees Similarly, a polyhedron is concave if its dihedral angles are all less than 180 degrees Note that this is not quite the same as nonconvex
A surface that is concave curves inwards in the middle. a concave stomach. convex. a concave surface is curved inwards in the middle convex (concavus, from com- ( COM-) + cavus )
Hollow and curved or rounded; vaulted; said of the interior of a curved surface or line, as of the curve of the of the inner surface of an eggshell, in opposition to convex; as, a concave mirror; the concave arch of the sky
A term to describe an outline which curves inward Synonymous with incurvate and the opposite of convex and excurvate Suggested that this term only be used to describe basal edges
Bending inward A concave lens or mirror has at least one side that bulges inward A concave lens produces diverging light rays See also reflect, refract, focal length, focal point
Wood that curves inwardly edge to edge when viewed from the face side, cupping or dished When the curve is pronounced, such material, especially very dry material, tends to split near the middle when fastened at the edges The best bet to save such material is by surface planing; first with the concave side up, then with the other side