• (a.) Having to opposite curvatures, that is, curved longitudinally in one direction and transversely in the opposite direction, as the surface of a saddle.
An`ti·clas'tic adjective [ Prefix anti- = Greek ... to break.] Having to opposite curvatures, that is, curved longitudinally in one direction and transversely in the opposite direction, as the surface of a saddle. 
(of a surface) having principal curvatures of opposite sign at a given point. Cf. synclastic.