Nonone \Non"one\, n. [Nonane + -one, suffix denoting the third degree of unsaturation.] (Chem.) 1. Any one of several metameric unsaturated hydrocarbons ({C9H14}) of the valylene series. [archaic?] [1913 Webster] 2. Any of several isomeric ketones ({C9H18O}) conceptually derived from nonane by substituting an oxygen for two hydrogen atoms on one of the non-terminal carbon atoms. [PJC]