heap has 22 distinct synonyms spread across 4 of its 6 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.
a collection of objects laid on top of each other
a car that is old and unreliable
“the fenders had fallen off that old bus”
bestow in large quantities
“He heaped him with work”
Synonyms, antonyms and the broader and narrower relations for heap come from Princeton University’s WordNet. Full sources and licences.
fill to overflow
“heap the platter with potatoes”