Source : Webster's Revised Unabridged Dictionary (1913)

Pseudosphere \Pseu"do*sphere`\, n. [Pseudo- + sphere.] (Geom.)
   The surface of constant negative curvature generated by the
   revolution of a tractrix. This surface corresponds in
   non-Euclidian space to the sphere in ordinary space. An
   important property of the surface is that any figure drawn
   upon it can be displaced in any way without tearing it or
   altering in size any of its elements.