The Collaborative International Dictionary of English v.0.48:

Purify \Pu"ri*fy\ (p[=u]"r[i^]*f[imac]), v. t. [imp. & p. p.
   Purified (p[=u]"r[i^]*f[imac]d); p. pr. & vb. n.
   Purifying (p[=u]"r[i^]*f[imac]"[i^]ng).] [F. purifier, L.
   purificare; purus pure + -ficare (in comp.) to make. See
   Pure, and -fy.]
   1. To make pure or clear from material defilement, admixture,
      or imperfection; to free from extraneous or noxious
      matter; as, to purify liquors or metals; to purify the
      blood; to purify the air.
      [1913 Webster]

   2. Hence, in figurative uses:
      (a) To free from guilt or moral defilement; as, to purify
          the heart.
          [1913 Webster]

                And fit them so
                Purified to receive him pure.     --Milton.
          [1913 Webster]
      (b) To free from ceremonial or legal defilement.
          [1913 Webster]

                And Moses took the blood, and put it upon the
                horns of the altar, . . . and purified the
                altar.                            --Lev. viii.
                                                  15.
          [1913 Webster]

                Purify both yourselves and your captives. --
                                                  Num. xxxi. 19.
          [1913 Webster]
      (c) To free from improprieties or barbarisms; as, to
          purify a language. --Sprat.
          [1913 Webster]

WordNet (r) 3.0 (2006):

purifying
    adj 1: serving to purge or rid of sin; "purgatorial rites" [syn:
           purgatorial, purging, purifying]
    2: freeing from noxious matter; "filtration is a purifying
       agent" [ant: adulterant, adulterating]
    3: acting like an antiseptic [syn: cleansing, purifying]

Moby Thesaurus II by Grady Ward, 1.0:

40 Moby Thesaurus words for "purifying":
   abstergent, apologetic, ascetic, atoning, cathartic, cleaning,
   cleansing, compensational, compensatory, depurative, detergent,
   diuretic, emetic, expiatory, expurgatory, lustral, lustrational,
   lustrative, penitential, piacular, propitiatory, purgative,
   purgatorial, purging, purificatory, reclamatory, recompensing,
   redeeming, redemptive, redressing, reparative, reparatory,
   repentant, repenting, restitutional, restitutive, restitutory,
   righting, satisfactional, squaring