late 14c., from O.Fr. decider, from L. decidere "to decide," lit. "to cut off," from de- "off" + cædere "to cut" (see cement). For L. vowel change, see acquisition. Sense is of resolving difficulties "at a stroke." Originally "to settle
a dispute;" meaning "to make up one's mind" is attested from 1830. Decided in the adj. sense of "resolute" is from 1790. Decisive is c.1600. A decided victory is one whose reality is not in doubt; a decisive one goes far toward settling some issue. Related: Decidedly (1790).