mutation

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun The act or process of being altered or changed.
• noun An alteration or change, as in nature, form, or quality.
• noun 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.
• noun 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.
• noun The nucleotide sequence, trait, or individual that results from such a change.
• noun 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.
• noun 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.

from The Century Dictionary.

• noun In biology:
• noun A sudden and inheritable change of type; a discontinuous variation; a sport.
• noun One of a group of individuals which originate directly and immediately from pure-bred stock and have uniform or nearly uniform characteristics different from those of the parents. Mutations differ in form from their parents in much the same manner as closely related species differ from each other. The seeds from a single plant of one of the evening primroses. Œnothcra Lamarckiana, often produce several mutations in the first generation.
• noun The act or process of changing; change; variableness.
• noun Rotation; succession.
• noun In phonetics, the change of a vowel through the influence of an a, i, or u in the following syllable: proposed for rendering German umlaut into English.
• noun In music:
• noun In medieval solmization, the change or passage from one hexachord to another, involving a change of the syllable applied to a given tone.
• noun In violin-playing, the shifting of the hand from one position to another.
• noun The change or alteration in a boy's voice at puberty.
• noun In French law, transfer by purchase or descent.
• noun A post-house.

from the GNU version of the Collaborative International Dictionary of English.

• noun Change; alteration, either in form or qualities.
• noun (Biol.) Gradual definitely tending variation, such as may be observed in a group of organisms in the fossils of successive geological levels.
• noun As now employed (first by de Vries), a cellular process resulting in a sudden inheritable variation (the offspring differing from its parents in some well-marked character or characters) as distinguished from a gradual variation in which the new characters become fully developed only in the course of many generations. The occurrence of mutations, the selection of strains carrying mutations permitting enhanced survival under prevailing conditions, and the mechanism of hereditary of the characters so appearing, are well-established facts; whether and to what extent the mutation process has played the most important part in the evolution of the existing species and other groups of organisms is an unresolved question.
• noun The result of the above process; a suddenly produced variation.
• noun (Biol.) a variant strain of an organism in which the hereditary variant property is caused by a mutation{3}.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun any alteration or change
• noun genetics Any heritable change of the base-pair sequence of genetic material
• noun a mutant
• noun linguistics an alteration a particular sound of a word, especially the initial consonant, which is triggered by the word's morphological or syntactic context and not by its phonological context
• noun this sense?) collective noun for a collection of thrushes

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun (genetics) any event that changes genetic structure; any alteration in the inherited nucleic acid sequence of the genotype of an organism
• noun (biology) an organism that has characteristics resulting from chromosomal alteration
• noun a change or alteration in form or qualities