principial

Principial is a seldom-attested adjective used in some English-language texts to denote something relating to a principle or to a fundamental rule. It is not widely recognized in major dictionaries, and there is no standard definition or fixed usage.

Etymologically, principial seems to derive from the Latin principium and from the English root principle, with the -al suffix. It is intended to mean “relating to a principle” rather than “main” or “prominent.”

Usage remains rare and concentrated in theoretical discourse. In philosophy or logic, a principial criterion or principle may be proposed to emphasize grounding in a fundamental rule, rather than practical or procedural considerations.

Principial is distinct from principal, which means main or head, and from principled, which describes adherence to moral or other explicit principles. In contrast, principial would function as a descriptive label for something pertaining to a principle, rather than signaling importance or principled behavior.

Because of its rarity, writers often substitute clearer terms such as fundamental, principle-based, or principled to avoid ambiguity. See also principal, principle, principled, principality, and principium.