defeatyoudaoicibaDictYouDict[defeat 词源字典]
defeat: [14] Etymologically, to defeat someone is literally to ‘undo’ them. The verb comes from Anglo–Norman defeter, a derivative of the noun defet. This in turn came from Old French desfait, the past participle of the verb desfaire. This was a descendant of medieval Latin disfacere, literally ‘undo’, a compound verb formed from the prefix dis-, denoting reversal, and Latin facere ‘do, make’.

Its original metaphorical extension was to ‘ruination’ or ‘destruction’, and the now central sense ‘conquer’ is not recorded in English before the 16th century. A classical Latin combination of facere with the prefix dē- rather than dis- produced defect, deficient, and deficit.
=> defect, deficient, deficit[defeat etymology, defeat origin, 英语词源]
defeat (v.)youdaoicibaDictYouDict
late 14c., from Anglo-French defeter, from Old French desfait, past participle of desfaire "to undo," from Vulgar Latin *diffacere "undo, destroy," from Latin dis- "un-, not" (see dis-) + facere "to do, perform" (see factitious). Original sense was of "bring ruination, cause destruction." Military sense of "conquer" is c. 1600. Related: Defeated; defeating.
defeat (n.)youdaoicibaDictYouDict
1590s, from defeat (v.).