mutagenPronunciation: /ˈmjuːtədʒ(ə)n/Definition of mutagen noun an agent, such as radiation or a chemical substance, which causes genetic mutation. Derivatives mutagenesisPronunciation: /-ˈdʒɛnɪsɪs/ noun mutagenicPronunciation: /-ˈdʒɛnɪk/ adjective mutagenicityPronunciation: /-ˈnɪsɪti/ noun Origin: 1940s: from mutation + -genmutagen in other Oxford dictionaries Definition of mutagen in the US English dictionary