gold rush has 7 distinct synonyms spread across 1 of its 2 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 sudden happening that brings good fortune (as a sudden opportunity to make money)
“the demand for testing has created a boom for those unregulated laboratories where boxes of specimen jars are processed like an assembly line”
a large migration of people to a newly discovered gold field
Synonyms, antonyms and the broader and narrower relations for gold rush come from Princeton University’s WordNet. Full sources and licences.