late 14c., "to quarrel, dispute," also "to combat, fight, make war" (senses now archaic), also "discuss, deliberate upon the pros and cons of," from Old French debatre (13c., Modern French débattre), originally "to fight," from de- "down, completely" (see de-) + batre "to beat," from Latin battuere "beat" (see batter (v.)).
And he began for to debate; He smote þe porter. ["Robert of Sicily," c. 1500]
Transitive sense of "to contend about in argument" is from mid-15c.; that of "argue for or against in public" is from 1520s. Related: Debated; debating.