Defeat
late Middle English (in the sense ‘undo, destroy, annul’): from Old French desfait ‘undone’, past participle of desfaire, from medieval Latin disfacere ‘undo’.
wiktionary
From Middle English defeten, from Middle English defet(“disfigured”, past participle) and defet(“defect”, noun), see Etymology 2 below.
From Middle English defet, from French deffet, desfait, past participle of the verb desfaire (compare modern French défaire), from des- + faire.
etymonline
defeat (v.)
late 14c., defeten, diffaiten, "overcome (with sorrow or anger)," 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," from PIE root *dhe- "to set, put."
From early 15c. as "bring ruination, cause destruction" (now obsolete in this sense); from late 15c. as "frustrate, prevent the success of." Sense of "deprive of something expected, desired or striven for" is from 1530s. Meaning "overcome in a contest of any kind" is from 1560s. Related: Defeated; defeating. Compare defect, deficient.
defeat (n.)
1590s, "an undoing, ruin," from defeat (v.). From c. 1600 as "act of overcoming in a military contest;" by 1690s of other contests and struggles.
