Heptane \Hep"tane\, n. [Gr. "epta` seven.] (Chem.) Any one of several isometric hydrocarbons, {C7H16}, of the paraffin series (nine are possible, four are known); -- so called because the molecule has seven carbon atoms. Specifically, a colorless liquid, found as a constituent of petroleum, in the tar oil of cannel coal, etc.