The Collaborative International Dictionary of English v.0.48:

absorbent \ab*sorb"ent\ ([a^]b*s[^o]rb"ent), a. [L. absorbens,
   p. pr. of absorbere.]
   Absorbing; swallowing; absorptive.
   [1913 Webster]

   Absorbent ground (Paint.), a ground prepared for a picture,
      chiefly with distemper, or water colors, by which the oil
      is absorbed, and a brilliancy is imparted to the colors.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Absorbent \Ab*sorb"ent\, n.
   1. Anything which absorbs. AS
      [1913 Webster]

            The ocean, itself a bad absorbent of heat. --Darwin.
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   2. (Med.) Any substance which absorbs and neutralizes acid
      fluid in the stomach and bowels, as magnesia, chalk, etc.;
      also a substance e. g., iodine which acts on the absorbent
      vessels so as to reduce enlarged and indurated parts. AS
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   3. pl. (Physiol.) The vessels by which the processes of
      absorption are carried on, as the lymphatics in animals,
      the extremities of the roots in plants. AS
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WordNet (r) 3.0 (2006):

absorbent
    adj 1: having power or capacity or tendency to absorb or soak up
           something (liquids or energy etc.); "as absorbent as a
           sponge" [syn: absorbent, absorptive] [ant:
           nonabsorbent, nonabsorptive]
    n 1: a material having capacity or tendency to absorb another
         substance [syn: absorbent material, absorbent]

Moby Thesaurus II by Grady Ward, 1.0:

21 Moby Thesaurus words for "absorbent":
   absorbency, absorption, adsorbent, adsorption, assimilation,
   blotter, blotting, blotting paper, chemisorption, chemosorption,
   digestion, endosmosis, engrossment, exosmosis, infiltration,
   osmosis, percolation, seepage, sorption, sponge, sponging