anticlastic

(mathematics) Having the property of a surface or portion of a surface whose two principal curvatures at each point have opposite signs, so that one normal section is concave and the other convex.

Of a double-curved surface, of which the two curvatures (transverse to each other) lie in opposite directions, convex in length and concave in breadth, or vice versa. This condition can be seen in e.g. a hyperbolic paraboloid roof. See synclastic.