expound

Expound is a verb meaning to explain in detail, to set forth and justify an idea, theory, or argument. It often connotes a thorough, systematic explanation rather than a brief summary.

Etymology traces expound to the Latin exponere “to put forth, set forth,” via Old French expoundre, with English usage emerging in the medieval period. The sense of laying out reasoning extended to detailed discussions.

Usage and nuance: Expound is formal and common in academic, legal, or philosophical discourse. It is typically transitive, taking a direct object such as “the theory” or “the plan,” and is often paired with on or upon to indicate the topic: expound on the evidence, expound upon the policy’s implications. It implies more depth and justification than a simple explanation.

Related terms and notes: Explication, exposition, elucidation, and elaboration are related but carry different nuances. A related noun is expounding or explication; expound itself is less colloquial than explain. In practice, writers may say, for example, “The author expounded his theory for the class” or “The report expounds the reasons for the reform.” Some style guides prefer expound on rather than expound about.