Source : Webster's Revised Unabridged Dictionary (1913)

Rigidity \Ri*gid"i*ty\, n. [L. rigiditas: cf. F. rigidit['e].
   See {Rigid}.]
   1. The quality or state of being rigid; want of pliability;
      the quality of resisting change of form; the amount of
      resistance with which a body opposes change of form; --
      opposed to {flexibility}, {ductility}, {malleability}, and
      {softness}.

   2. Stiffness of appearance or manner; want of ease or
      elegance. --Sir H. Wotton.

   3. Severity; rigor. [Obs. orR.] --Bp. Burnet.

   Syn: Stiffness; rigidness; inflexibility.

Source : WordNet®

rigidity
     n 1: the physical property of being stiff and resisting bending
          [syn: {rigidness}]
     2: the quality of being rigid and rigorously severe [syn: {inflexibility}]
        [ant: {flexibility}]