The Collaborative International Dictionary of English v.0.48:

Persistence \Per*sist"ence\, Persistency \Per*sist"en*cy\, n.
   [See Persistent.]
   1. The quality or state of being persistent; staying or
      continuing quality; hence, in an unfavorable sense,
      doggedness; obstinacy.
      [1913 Webster]

   2. The continuance of an effect after the cause which first
      gave rise to it is removed; as:
      (a) (Physics) The persistence of motion.
      (b) (Physiol.) Visual persistence, or persistence of the
          visual impression; auditory persistence, etc.
          [1913 Webster]

WordNet (r) 3.0 (2006):

persistency
    n 1: persistent determination [syn: doggedness,
         perseverance, persistence, persistency, tenacity,
         tenaciousness, pertinacity]