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.
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):
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:
3: (of color) not chromatically pure; diluted; "an unsaturated
red" [ant: pure, saturated]