1. To win victory over; beat.
2. To prevent the success of; thwart: Internal strife defeats the purpose of teamwork.
3. Law To make void; annul.

1. The act of defeating or state of being defeated.
2. Failure to win.
3. A coming to naught; frustration: the defeat of a lifelong dream.
4. Law The act of making null and void.

Synonyms: These verbs mean to triumph over an adversary. Defeat is the most general: "Whether we defeat the enemy in one battle, or by degrees, the consequences will be the same" (Thomas Paine).
Conquer suggests decisive and often wide-scale victory: "The Franks . . . having conquered the Gauls, established the kingdom which has taken its name from them" (Alexander Hamilton).
Vanquish emphasizes total mastery: Napoleon's forces were vanquished at Waterloo.
Beat is similar to defeat, though less formal and often more emphatic: "To win battles . . . you beat the soul . . . of the enemy man" (George S. Patton).
Rout implies complete victory followed by the disorderly flight of the defeated force: The enemy was routed in the first battle.
Subdue suggests mastery and control achieved by overpowering: "It cost [the Romans] two great wars, and three great battles, to subdue that little kingdom [Macedonia]" (Adam Smith).
Subjugate more strongly implies reducing an opponent to submission: "The last foreigner to subjugate England was a Norman duke in the Middle Ages named William" (Stanley Meisler).
To overcome is to prevail over, often by persevering: He overcame his injury after months of physical therapy.