late 14c., deffinen, diffinen, "to specify; to fix or establish authoritatively;" of words, phrases, etc., "state the signification of, explain what is meant by, describe in detail," from Old French defenir, definir "to finish, conclude, come to an end; bring to an end; define, determine with precision," and directly from Medieval Latin diffinire, definire, from Latin definire "to limit, determine, explain," from de "completely" (see de-) + finire "to bound, limit," from finis "boundary, end" (see finish (v.)). From c. 1400 as "determine, declare, or mark the limit of." Related: Defined; defining.