clump has 18 distinct synonyms spread across 7 of its 7 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.
come together as in a cluster or flock
“The poets constellate in this town every summer”
gather or cause to gather into a cluster
“She bunched her fingers into a fist”
a grouping of a number of similar things
“a bunch of trees”
Synonyms, antonyms and the broader and narrower relations for clump come from Princeton University’s WordNet. Full sources and licences.