Definiens

Definiens is a term used in logic, philosophy, and linguistics to refer to the part of a definition that provides the sense or description that defines a term. In a typical definitional sentence, the definiendum is the word or expression being defined, while the definiens is the description that assigns its meaning. Example: "A square is a rectangle with equal sides." Here, "square" is the definiendum, and "a rectangle with equal sides" is the definiens. The definiens explains the concept in terms of more basic concepts or properties.

Etymology and related terms: The word comes from Latin definiens, the present participle of definire, meaning "defining." The related term definiendum refers to the thing to be defined. The pair is used to distinguish the term being defined from the description that defines it.

Usage and significance: The distinction helps formalize definitions across disciplines. In mathematical and scientific definitions, the definiens often provides a concise statement of necessary and sufficient conditions. Definitions may be informative, stipulative, operational, or ostensive; in each case the definiens conveys the criterion by which instances are recognized. Cautions include avoiding circular definitions, where the definiens presupposes the definiendum, and striving for precision to prevent ambiguity or vagueness.

See also: definiendum, definition, genus proximum and differentia, ostensive definition, stipulative definition, terminography.