The Collaborative International Dictionary of English v.0.48:

Regeneration \Re*gen`er*a"tion\ (-?"sh?n), n. [L. regeneratio:
   cf. F. r['e]g['e]neration.]
   1. The act of regenerating, or the state of being
      regenerated.
      [1913 Webster]

   2. (Theol.) The entering into a new spiritual life; the act
      of becoming, or of being made, Christian; that change by
      which holy affectations and purposes are substituted for
      the opposite motives in the heart.
      [1913 Webster]

            He saved us by the washing of regeneration, and
            renewing of the Holy Chost.           --Tit. iii. 5.
      [1913 Webster]

   3. (Biol.) The reproduction of a part which has been removed
      or destroyed; re-formation; -- a process especially
      characteristic of a many of the lower animals; as, the
      regeneration of lost feelers, limbs, and claws by spiders
      and crabs.
      [1913 Webster]

   4. (Physiol.)
      (a) The reproduction or renewal of tissues, cells, etc.,
          which have been used up and destroyed by the ordinary
          processes of life; as, the continual regeneration of
          the epithelial cells of the body, or the regeneration
          of the contractile substance of muscle.
      (b) The union of parts which have been severed, so that
          they become anatomically perfect; as, the regeneration
          of a nerve.
          [1913 Webster]

WordNet (r) 3.0 (2006):

regeneration
    n 1: (biology) growth anew of lost tissue or destroyed parts or
         organs
    2: feedback in phase with (augmenting) the input [syn: positive
       feedback, regeneration]
    3: the activity of spiritual or physical renewal
    4: forming again (especially with improvements or removal of
       defects); renewing and reconstituting [syn: re-formation,
       regeneration]