The Collaborative International Dictionary of English v.0.48:

Ablution \Ab*lu`tion\, n. [L. ablutio, fr. abluere: cf. F.
   ablution. See Abluent.]
   1. The act of washing or cleansing; specifically, the washing
      of the body, or some part of it, as a religious rite.
      [1913 Webster]

   2. The water used in cleansing. "Cast the ablutions in the
      main." --Pope.
      [1913 Webster]

   3. (R. C. Ch.) A small quantity of wine and water, which is
      used to wash the priest's thumb and index finger after the
      communion, and which then, as perhaps containing portions
      of the consecrated elements, is drunk by the priest.
      [1913 Webster]

WordNet (r) 3.0 (2006):

ablution
    n 1: the ritual washing of a priest's hands or of sacred vessels

Moby Thesaurus II by Grady Ward, 1.0:

34 Moby Thesaurus words for "ablution":
   cleaning out, douche, douching, elution, elutriation, enema, flush,
   flushing, flushing out, irrigation, lathering, lavabo, lavage,
   lavation, laving, mopping, mopping up, rinse, rinsing, scouring,
   scrub, scrubbing, scrubbing up, shampoo, soaping, sponge, sponging,
   swabbing, wash, washing, washing up, washout, washup, wiping up



Easton's 1897 Bible Dictionary:

Ablution
   or washing, was practised, (1.) When a person was initiated into
   a higher state: e.g., when Aaron and his sons were set apart to
   the priest's office, they were washed with water previous to
   their investiture with the priestly robes (Lev. 8:6).

     (2.) Before the priests approached the altar of God, they were
   required, on pain of death, to wash their hands and their feet
   to cleanse them from the soil of common life (Ex. 30:17-21). To
   this practice the Psalmist alludes, Ps. 26:6.

     (3.) There were washings prescribed for the purpose of
   cleansing from positive defilement contracted by particular
   acts. Of such washings eleven different species are prescribed
   in the Levitical law (Lev. 12-15).

     (4.) A fourth class of ablutions is mentioned, by which a
   person purified or absolved himself from the guilt of some
   particular act. For example, the elders of the nearest village
   where some murder was committed were required, when the murderer
   was unknown, to wash their hands over the expiatory heifer which
   was beheaded, and in doing so to say, "Our hands have not shed
   this blood, neither have our eyes seen it" (Deut. 21:1-9). So
   also Pilate declared himself innocent of the blood of Jesus by
   washing his hands (Matt. 27:24). This act of Pilate may not,
   however, have been borrowed from the custom of the Jews. The
   same practice was common among the Greeks and Romans.

     The Pharisees carried the practice of ablution to great
   excess, thereby claiming extraordinary purity (Matt. 23:25).
   Mark (7:1-5) refers to the ceremonial ablutions. The Pharisees
   washed their hands "oft," more correctly, "with the fist" (R.V.,
   "diligently"), or as an old father, Theophylact, explains it,
   "up to the elbow." (Compare also Mark 7:4; Lev. 6:28; 11: 32-36;
   15:22) (See WASHING.)