frequently has 4 distinct synonyms spread across 1 of its 1 sense. 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 infrequently.
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.
many times at short intervals
“we often met over a cup of coffee”
Synonyms, antonyms and the broader and narrower relations for frequently come from Princeton University’s WordNet. Full sources and licences.