research has 4 distinct synonyms spread across 2 of its 4 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. WordNet records no antonym for it — antonymy is a relation between word forms rather than concepts, so it is deliberately sparse.
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.
systematic investigation to establish facts
a search for knowledge
“their pottery deserves more research than it has received”
attempt to find out in a systematically and scientific manner
“The student researched the history of that word”
inquire into
“the students had to research the history of the Second World War for their history project”
Synonyms, antonyms and the broader and narrower relations for research come from Princeton University’s WordNet. Full sources and licences.