From The Collaborative International Dictionary of English v.0.48 [gcide]:
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]
From WordNet (r) 3.0 (2006) [wn]:
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