used has 6 distinct synonyms spread across 2 of its 3 senses. Each sense below keeps its own list, because a synonym belongs to a meaning and not to a word: swapping one sense's substitute into another sense's sentence is how a thesaurus makes writing worse. Its one recorded opposite is misused.
Counts are distinct word forms across every sense. A synonym that appears under three senses is counted once here and shown three times below, under each sense it belongs to.
employed in accomplishing something
“the principle of surprise is the most used and misused of all the principles of war”
(of persons) taken advantage of
“after going out of his way to help his friend get the job he felt not appreciated but used”
Synonyms, antonyms and the broader and narrower relations for used come from Princeton University’s WordNet. Full sources and licences.