late 14c., mutacioun, "action or process of changing," from Old French mutacion (13c.), and directly from Latin mutationem (nominative mutatio) "a changing, alteration, a turn for the worse," noun of action from past-participle stem of mutare "to change" (from PIE root *mei- (1) "to change, go, move"). The genetics sense "process whereby heritable changes in DNA arise" is from 1894. The linguist's i-mutation is attested from 1874; earlier was i-umlaut (1869), from German, for which mutation was Sweet's English substitute.
word-forming element technically meaning "something produced," but mainly, in modern use, "thing that produces or causes," from French -gène (18c.), from Greek -genes "born of, produced by," which is from the same source as genos "birth," genea "race, family," from PIE root *gene- "give birth, beget," with derivatives referring to procreation and familial and tribal groups. First used in late 18th century French chemistry (see oxygen), it probably involves a misunderstanding of -genes, as though it meant "that which produces."
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Definitions of mutagen from WordNet
any agent (physical or environmental) that can induce a genetic mutation or can increase the rate of mutation;