The Collaborative International Dictionary of English v.0.48:

Penitence \Pen"i*tence\, n. [F. p['e]nitence, L. paenitentia.
   See Penitent, and cf. Penance.]
   The quality or condition of being penitent; the disposition
   of a penitent; sorrow for sins or faults; repentance;
   contrition. "Penitence of his old guilt." --Chaucer.
   [1913 Webster]

         Death is deferred, and penitenance has room
         To mitigate, if not reverse, the doom.   --Dryden.
   [1913 Webster]

   Syn: Repentance; contrition; compunction.
        [1913 Webster]

WordNet (r) 3.0 (2006):

penitence
    n 1: remorse for your past conduct [syn: repentance,
         penitence, penance]

Moby Thesaurus II by Grady Ward, 1.0:

59 Moby Thesaurus words for "penitence":
   Day of Atonement, Yom Kippur, abject apology, acknowledgment,
   anguish, apology, asceticism, attrition, breast-beating,
   change of heart, cold purgatorial fires, compunction, confession,
   contriteness, contrition, deathbed repentance, debasement,
   degradation, distress, excuse, fasting, flagellation, grief,
   hair shirt, heartfelt apology, humbling, humiliation, lustration,
   maceration, mea culpa, mortification, penance, penitential act,
   penitential exercise, penitently, purgation, purgatory, qualm,
   reformation, regret, regretfulness, regrets, remorse,
   remorsefulness, repentance, rue, ruefulness, ruth,
   sackcloth and ashes, sadness, saeta, scruple, self-accusation,
   self-punishment, self-reproach, shame, sorrow, sorrowfulness,
   wearing a hairshirt