The Collaborative International Dictionary of English v.0.48:

Apposition \Ap`po*si"tion\, n. [L. appositio, fr. apponere: cf.
   F. apposition. See Apposite.]
   1. The act of adding; application; accretion.
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            It grows . . . by the apposition of new matter.
                                                  --Arbuthnot.
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   2. The putting of things in juxtaposition, or side by side;
      also, the condition of being so placed.
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   3. (Gram.) The state of two nouns or pronouns, put in the
      same case, without a connecting word between them; as, I
      admire Cicero, the orator. Here, the second noun explains
      or characterizes the first.
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   Growth by apposition (Physiol.), a mode of growth
      characteristic of non vascular tissues, in which nutritive
      matter from the blood is transformed on the surface of an
      organ into solid unorganized substance.
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WordNet (r) 3.0 (2006):

apposition
    n 1: a grammatical relation between a word and a noun phrase
         that follows; "`Rudolph the red-nosed reindeer' is an
         example of apposition"
    2: (biology) growth in the thickness of a cell wall by the
       deposit of successive layers of material
    3: the act of positioning close together (or side by side); "it
       is the result of the juxtaposition of contrasting colors"
       [syn: juxtaposition, apposition, collocation]