The Collaborative International Dictionary of English v.0.48:

Assimilate \As*sim"i*late\, v. i.
   1. To become similar or like something else. [R.]
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   2. To change and appropriate nourishment so as to make it a
      part of the substance of the assimilating body.
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            Aliment easily assimilated or turned into blood.
                                                  --Arbuthnot.
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   3. To be converted into the substance of the assimilating
      body; to become incorporated; as, some kinds of food
      assimilate more readily than others.
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            I am a foreign material, and cannot assimilate with
            the church of England.                --J. H.
                                                  Newman.
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The Collaborative International Dictionary of English v.0.48:

Assimilate \As*sim"i*late\, v. t. [imp. & p. p. Assimilated;
   p. pr. & vb. n. Assimilating.] [L. assimilatus, p. p. of
   assimilare; ad + similare to make like, similis like. See
   Similar, Assemble, Assimilate.]
   1. To bring to a likeness or to conformity; to cause a
      resemblance between. --Sir M. Hale.
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            To assimilate our law to the law of Scotland. --John
                                                  Bright.
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            Fast falls a fleecy; the downy flakes
            Assimilate all objects.               --Cowper.
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   2. To liken; to compa?e. [R.]
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   3. To appropriate and transform or incorporate into the
      substance of the assimilating body; to absorb or
      appropriate, as nourishment; as, food is assimilated and
      converted into organic tissue.
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            Hence also animals and vegetables may assimilate
            their nourishment.                    --Sir I.
                                                  Newton.
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            His mind had no power to assimilate the lessons.
                                                  --Merivale.
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WordNet (r) 3.0 (2006):

assimilate
    v 1: take up mentally; "he absorbed the knowledge or beliefs of
         his tribe" [syn: absorb, assimilate, ingest, take
         in]
    2: become similar to one's environment; "Immigrants often want
       to assimilate quickly" [ant: dissimilate]
    3: make similar; "This country assimilates immigrants very
       quickly" [ant: dissimilate]
    4: take (gas, light or heat) into a solution [syn: assimilate,
       imbibe]
    5: become similar in sound; "The nasal assimilates to the
       following consonant" [ant: dissimilate]