ADJECTIVE (3)

1. not saturated; capable of dissolving more of a substance at a given temperature;
- Example: "an unsaturated salt solution"

2. used of a compound (especially of carbon) containing atoms sharing more than one valence bond;
- Example: "unsaturated fats"

3. (of color) not chromatically pure; diluted;
- Example: "an unsaturated red"

The Collaborative International Dictionary of English v.0.48:

Unsaturated \Un*sat"u*ra`ted\, a.
   1. Capable of absorbing or dissolving to a greater degree;
      as, an unsaturated solution.
      [1913 Webster]

   2. (Chem.) Capable of taking up, or of uniting with, certain
      other elements or compounds, without the elimination of
      any side product; thus, aldehyde, ethylene, and ammonia
      are unsaturated; benzene has three unsaturated bonds. The
      term is applied most commonly to compounds with a double
      or triple bond between two carbon atoms (as in ethylene).
      [1913 Webster +PJC]

WordNet (r) 3.0 (2006):

unsaturated
    adj 1: not saturated; capable of dissolving more of a substance
           at a given temperature; "an unsaturated salt solution"
           [ant: concentrated, saturated]
    2: used of a compound (especially of carbon) containing atoms
       sharing more than one valence bond; "unsaturated fats" [ant:
       saturated]
    3: (of color) not chromatically pure; diluted; "an unsaturated
       red" [ant: pure, saturated]