The Collaborative International Dictionary of English v.0.48:

Immovability \Im*mov"a*bil"i*ty\, n.
   The quality or state of being immovable; fixedness;
   steadfastness; as, immovability of a heavy body; immovability
   of purpose.
   [1913 Webster]

WordNet (r) 3.0 (2006):

immovability
    n 1: not capable of being moved or rearranged [syn:
         immovability, immovableness] [ant: movability,
         movableness]