1. a similarity between two entities in certain limited respects. In biology, it refers to similarity of function in structures with different evolutionary origins, such as wings in bats and butterflies. See also homology; homoplasy.

2. a method of argument that relies on an inference that a similarity between two or more entities in some attributes justifies a probable assumption that they will be similar in other attributes (see false analogy). Analogy is often used in arguments about the existence of God and of other minds.

3. in linguistics, the process by which the regular patterns of inflection, word formation, and the like in a language are extended to novel or anomalous instances. This can be observed in historical language change as well as in language acquisition. A notable form of analogy occurs when children regularize irregular grammatical forms, such as applying the -ed past-tense ending to irregular verbs, creating novel forms such as go-ed. —analogical adj. —analogous adj.