Thoroughly DEFEAT can be defined as two separate words, 'THOROUGHLY' and 'DEFEAT'. To THOROUGHLY DEFEAT someone or something means to completely and utterly DEFEAT them. Two crossword solutions for this term are 'TROUNCE' (7 letters) and 'VANQUISH' (8 letters). TROUNCE is a verb meaning to DEFEAT someone or something decisively and conclusively. VANQUISH is also a verb meaning to DEFEAT someone or something in a battle or contest. Both words imply a complete and total victory over the opponent.