The Collaborative International Dictionary of English v.0.48:

Changeless \Change"less\, a.
   That can not be changed; constant; as, a changeless purpose.
   -- Change"less*ness, n.
   [1913 Webster]

WordNet (r) 3.0 (2006):

changelessness
    n 1: the property of remaining unchanged
    2: the quality of being unchangeable; having a marked tendency
       to remain unchanged [syn: changelessness,
       unchangeability, unchangeableness, unchangingness]
       [ant: changeability, changeableness]