undefinitional

Undefinitional is an adjective used to describe terms, concepts, or statements that lack a precise or universally agreed definition within a particular theoretical framework. The designation does not imply that the term cannot be discussed, only that its meaning is not captured by a formal definition constructed from other terms in the system. In many formal theories, some terms are treated as undefined or primitive; their meaning is supplied by axioms and informal understanding rather than by definitions that derive from more basic terms. This approach avoids circularity and establishes a foundation for deductive reasoning.

In philosophy of language and logic, the claim that certain notions are undefinitional is debated. Some theories embrace primitive notions and ostensive or pragmatic definitions for reference, while others argue that all genuine terms can be defined in principle, given sufficient expressive resources. The idea of undefinitional terms is closely linked to the notion of definability limits and to the distinction between semantic content and pragmatic use.

Common examples appear in geometry, where points, lines, and planes are often treated as undefined terms that are explained through axioms and models rather than explicit definitions. In broader discussions, concepts such as truth, consciousness, or justice are sometimes discussed as candidates for indefinability within particular frameworks.

Related concepts include definability, primitive terms, undefinable, axioms, and ostensive definitions.