n. In mathematics, an equation between ratios.n. An agreement, likeness, or proportion between the relations of things to one another; hence, often, agreement or likeness of things themselves.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.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.n. In biology, resemblance without affinity; physiological or adaptive likeness between things morphologically or structurally unlike: the opposite of homology.