think has 18 distinct synonyms spread across 5 of its 14 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.
use or exercise the mind or one's power of reason in order to make inferences, decisions, or arrive at a solution or judgments
“I've been thinking all day and getting nowhere”
imagine or visualize
“Just think--you could be rich one day!”
focus one's attention on a certain state
“Think big”
bring into a given condition by mental preoccupation
“She thought herself into a state of panic over the final exam”
an instance of deliberate thinking
“I need to give it a good think”
5 of the 14 recorded senses carry no synonym, antonym or related term, so they are not shown above. Every sense, with its definition and examples, is on the full entry for think.
Synonyms, antonyms and the broader and narrower relations for think come from Princeton University’s WordNet. Full sources and licences.