Source : Webster's Revised Unabridged Dictionary (1913)

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.

   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.

Source : WordNet®

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