rotenonePronunciation: /ˈrəʊtənəʊn/Definition of rotenone noun [mass noun] Chemistry a toxic crystalline substance obtained from the roots of derris and related plants, widely used as an insecticide. A polycyclic ketone; chemical formula: C23H22O6 Origin: 1920s: from Japanese rotenon (from roten 'derris') + -onerotenone in other Oxford dictionaries Definition of rotenone in the US English dictionary