discomfit (v.)

c. 1200, discomfiten, "to undo in battle, defeat, overthrow," from Anglo-French descomfiter, Old French desconfire "to defeat, destroy," from des- "not" (see dis-) + confire "make, prepare, accomplish," from Latin conficere "to prepare," from com- "with" (see com-) + combining form of facere "to make, to do" (from PIE root *dhe- "to set, put").

General sense of "defeat or overthrow the plans or purposes of" is from late 14c. Weaker sense of "disconcert" is first recorded 1520s in English, probably by confusion with discomfort. Related: Discomfited; discomfiting.