To vanquish means to defeat someone completely and decisively. When an army vanquishes its enemy, it doesn't just win a close battle: it overwhelms and conquers them thoroughly. When a chess champion vanquishes her opponent, she doesn't just edge out a victory: she dominates the match.

The word carries a sense of total victory, often after a difficult struggle. A scientist might vanquish a disease by discovering a cure that eliminates it entirely. A debate team vanquishes its rivals by winning the championship after months of hard work and preparation.

Vanquished is the past tense and can also be used as an adjective, describing someone or something that has been thoroughly defeated. In stories and history, you'll often read about vanquished armies retreating from battle, or vanquished kingdoms falling to conquerors. The vanquished foe in a legend might surrender completely or flee in defeat.

The word has an old-fashioned, dramatic quality to it. You probably wouldn't say you vanquished your brother at checkers, but you might read about knights vanquishing dragons in medieval tales, or explorers vanquishing the challenges of crossing unknown territories.