The Collaborative International Dictionary of English v.0.48:

Staleness \Stale"ness\, n.
   The quality or state of being stale.
   [1913 Webster]

WordNet (r) 3.0 (2006):

staleness
    n 1: unoriginality as a result of being dull and hackneyed [syn:
         triteness, staleness]
    2: having lost purity and freshness as a consequence of aging
       [ant: freshness]