analogy

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. Similarity in some respects between things that are otherwise dissimilar.
2. n. A comparison based on such similarity. See Synonyms at likeness.
3. n. Biology Correspondence in function or position between organs of dissimilar evolutionary origin or structure.
4. n. A form of logical inference or an instance of it, based on the assumption that if two things are known to be alike in some respects, then they must be alike in other respects.
5. n. Linguistics The process by which words or morphemes are re-formed or created on the model of existing grammatical patterns in a language, often leading to greater regularity in paradigms, as evidenced by helped replacing holp and holpen as the past tense and past participle of help on the model of verbs such as yelp, yelped, yelped.

Century Dictionary and Cyclopedia

1. n. In mathematics, an equation between ratios. This use is obsolete except in a few phrases, as Napier's analogies, which are four important formulas of spherical trigonometry.
2. n. An agreement, likeness, or proportion between the relations of things to one another; hence, often, agreement or likeness of things themselves. Analogy strictly denotes only a partial similarity, as in some special circumstances or effects predicable of two or more things in other respects essentially different: thus, when we say that learning enlightens the mind, we recognize an analogy between learning and light, the former being to the mind what the latter is to the eye, enabling it to discover things before hidden.
3. n. Specifically In logic, a form of reasoning in which, from the similarity of two or more things in certain particulars, their similarity in other particulars is inferred. Thus, the earth and Mars are both planets, nearly equidistant from the sun, not differing greatly in density, having similar distributions of seas and continents, alike in conditions of humidity, temperature, seasons, day and night, etc.; but the earth also supports organic life; hence Mars (probably) supports organic life—is an argument from analogy. See induction.
4. n. In grammar, conformity to the spirit, structure, or general rules of a language; similarity as respects any of the characteristics of a language, as derivation, inflection, spelling, pronunciation, etc.
5. n. In biology, resemblance without affinity; physiological or adaptive likeness between things morphologically or structurally unlike: the opposite of homology. Thus, there is an analogy between the wing of a bird and that of a butterfly, both being adapted to the same physiological purpose of flight, but there is no morphological relation between them. Analogy rests upon mere functional (that is, physiological) modifications; homology is grounded upon structural (that is, morphological) identity or unity. Analogy is the correlative of physiology, homology of morphology; but the two may be coincident, as when structures identical in morphology are used for the same purposes and are therefore physiologically identical.

Wiktionary

1. n. A relationship of resemblance or equivalence between two situations, people, or objects, especially when used as a basis for explanation or extrapolation.

GNU Webster's 1913

1. n. A resemblance of relations; an agreement or likeness between things in some circumstances or effects, when the things are otherwise entirely different. Thus, learning enlightens the mind, because it is to the mind what light is to the eye, enabling it to discover things before hidden.
2. n. (Biol.) A relation or correspondence in function, between organs or parts which are decidedly different.
3. n. (Geom.) Proportion; equality of ratios.
4. n. (Gram.) Conformity of words to the genius, structure, or general rules of a language; similarity of origin, inflection, or principle of pronunciation, and the like, as opposed to anomaly.

WordNet 3.0

1. n. an inference that if things agree in some respects they probably agree in others
2. n. drawing a comparison in order to show a similarity in some respect
3. n. the religious belief that between creature and creator no similarity can be found so great but that the dissimilarity is always greater; any analogy between God and humans will always be inadequate