1. The act or process of being altered or changed.
2. An alteration or change, as in nature, form, or quality.
a. A change in the nucleotide sequence of the genome of an organism or virus, sometimes resulting in the appearance of a new character or trait not found in the parental type.
b. The process by which such a change occurs, either through an alteration in the nucleotide sequence coding for a gene or through a change in the physical arrangement of the genetic material.
c. The nucleotide sequence, trait, or individual that results from such a change.
a. A change affecting a sound or a class of sounds, such as back vowels or plosive consonants, through assimilation to another sound, as in the process of umlaut.
b. A change affecting a sound or a class of sounds that is conditioned by morphological or syntactic factors rather than purely phonological factors, as in Irish, where certain words cause the lenition of the initial consonants of the following word.
[Middle English mutacioun, from Old French mutacion, from Latin mūtātiō, mūtātiōn-, from past participle of mūtāre, to change; see MUTATE.]
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2020 by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Indo-European & Semitic Roots Appendices
Thousands of entries in the dictionary include etymologies that trace their origins back to reconstructed proto-languages. You can obtain more information about these forms in our online appendices:
The Indo-European appendix covers nearly half of the Indo-European roots that have left their mark on English words. A more complete treatment of Indo-European roots and the English words derived from them is available in our Dictionary of Indo-European Roots.