purposeless has 5 distinct synonyms spread across 1 of its 2 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 purposeful.
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.
not evidencing any purpose or goal
serving no useful purpose; having no excuse for being
“otiose lines in a play”
Synonyms, antonyms and the broader and narrower relations for purposeless come from Princeton University’s WordNet. Full sources and licences.