(biology) an organism that has characteristics resulting from chromosomal alteration WordNet 3.0 & Open English WordNet

In biology, and especially in genetics, a mutant is an organism or a new genetic character arising or resulting from an instance of mutation, which is generally an alteration of the DNA sequence of the genome or chromosome of an organism. Wikipedia

Biological entity which has undergone a change in its genetic structure. Wikipedia Disambiguation

A change in the chemical constitution of the DNA in the chromosomes of an organism. OmegaWiki

An individual bearing an allele that has undergone mutation and is expressed in the phenotype. OmegaWiki

Something which has mutated, which has one or more new characteristics from a mutation. Wiktionary

A plant or an animal, or part of a plant or animal, which has some peculiarity not usually seen in the species; an abnormal variety or growth. The term encompasses both mutants and organisms with non-genetic developmental abnormalities such as birth defects. Wiktionary

Abnormal plant or animal. Wiktionary (translation)