The Collaborative International Dictionary of English v.0.48:

Purification \Pu`ri*fi*ca"tion\, n. [F. purification, L.
   purificatio. See Purify.]
   1. The act of purifying; the act or operation of separating
      and removing from anything that which is impure or
      noxious, or heterogeneous or foreign to it; as, the
      purification of liquors, or of metals.
      [1913 Webster]

   2. The act or operation of cleansing ceremonially, by
      removing any pollution or defilement.
      [1913 Webster]

            When the days of her purification according to the
            law of Moses were accomplished.       --Luke ii. 22.
      [1913 Webster]

   3. A cleansing from guilt or the pollution of sin; the
      extinction of sinful desires, appetites, and inclinations.
      [1913 Webster]

WordNet (r) 3.0 (2006):

purification
    n 1: the act of cleaning by getting rid of impurities
    2: the process of removing impurities (as from oil or metals or
       sugar etc.) [syn: refining, refinement, purification]
    3: a ceremonial cleansing from defilement or uncleanness by the
       performance of appropriate rites [syn: purification,
       purgation]
    4: the act of purging of sin or guilt; moral or spiritual
       cleansing; "purification through repentance"

Moby Thesaurus II by Grady Ward, 1.0:

96 Moby Thesaurus words for "purification":
   ablation, abrasion, absolution, abstersion, abstraction, atonement,
   beatification, beatitude, blessedness, blessing, bolting,
   bowdlerization, canonization, catharsis, clarification, cleaning,
   cleansing, colature, concentrate, concentration, consecration,
   decoction, dedication, deduction, destructive distillation,
   detersion, devotion, disentanglement, disinvolvement, distillate,
   distillation, dry cleaning, edulcoration, elixir, elution,
   elutriation, enshrinement, erosion, essence, essentialization,
   exaltation, expiation, expurgation, extract, extraction, filtering,
   filtration, forgiveness, glorification, grace, hallowing, infusion,
   justification, justification by works, leaching, lixiviation,
   lustration, narrowing, percolation, purgation, purge, purging,
   quintessence, rebirth, redemption, refinement, regeneration,
   removal, riddling, sainthood, sainting, salvation, sanctification,
   screening, separation, setting apart, sieving, sifting,
   simplification, spirit, spiritualization, state of grace,
   steam cleaning, straining, streamlining, stripping, stripping down,
   subduction, sublation, sublimation, subtraction, taking away,
   uncluttering, unscrambling, unsnarling, winnowing



Easton's 1897 Bible Dictionary:

Purification
   the process by which a person unclean, according to the
   Levitical law, and thereby cut off from the sanctuary and the
   festivals, was restored to the enjoyment of all these
   privileges.

     The great annual purification of the people was on the Day of
   Atonement (q.v.).

     But in the details of daily life there were special causes of
   cermonial uncleanness which were severally provided for by
   ceremonial laws enacted for each separate case. For example, the
   case of the leper (Lev. 13, 14), and of the house defiled by
   leprosy (14:49-53; see also Matt. 8:2-4). Uncleanness from
   touching a dead body (Num. 19:11; Hos. 9:4; Hag. 2:13; Matt.
   23:27; Luke 11:44). The case of the high priest and of the
   Nazarite (Lev. 21:1-4, 10, 11; Num. 6:6, 7; Ezek. 44:25).
   Purification was effected by bathing and washing the clothes
   (Lev. 14:8, 9); by washing the hands (Deut. 21:6; Matt. 27:24);
   washing the hands and feet (Ex. 30:18-21; Heb. 6:2, "baptisms",
   R.V. marg., "washings;" 9:10); sprinkling with blood and water
   (Ex. 24:5-8; Heb. 9:19), etc. Allusions to this rite are found
   in Ps. 26:6; 51:7; Ezek. 36:25; Heb. 10:22.