The Collaborative International Dictionary of English v.0.48:

Permanence \Per"ma*nence\, Permanency \Per"ma*nen*cy\, n. [Cf.
   F. permanence.]
   The quality or state of being permanent; continuance in the
   same state or place; duration; fixedness; as, the permanence
   of institutions; the permanence of nature.
   [1913 Webster]

WordNet (r) 3.0 (2006):

permanency
    n 1: the property of being able to exist for an indefinite
         duration [syn: permanence, permanency] [ant:
         impermanence, impermanency]