401-k plan has 1 distinct synonym 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. 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 retirement savings plan that is funded by employee contributions and (often) matching contributions from the employer; contributions are made from your salary before taxes and the funds grow tax-free until they are withdrawn, at which point they can be converted into an IRA; funds can be transferred if you change employers and you can (to some extent) manage the investments yourself
Synonyms, antonyms and the broader and narrower relations for 401-k plan come from Princeton University’s WordNet. Full sources and licences.