I·so- Is- A prefix or combining form, indicating identity, or equality; the same numerical value; as in isopod, isomorphous, isochromatic. Specif.: (a) Chem. Applied to certain compounds having the same composition but different properties; as in isocyanic. (b) Organic Chem. Applied to compounds of certain isomeric series in whose structure one carbon atom, at least, is connected with three other carbon atoms; -- contrasted with neo- and normal; as in isoparaffine; isopentane.
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