jack has 27 distinct synonyms spread across 9 of its 14 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.
someone who works with their hands; someone engaged in manual labor
immense East Indian fruit resembling breadfruit; it contains an edible pulp and nutritious seeds that are commonly roasted
a small ball at which players aim in lawn bowling
an electrical device consisting of a connector socket designed for the insertion of a plug
game equipment consisting of one of several small six-pointed metal pieces that are picked up while bouncing a ball in the game of jacks
small flag indicating a ship's nationality
tool for exerting pressure or lifting
any of several fast-swimming predacious fishes of tropical to warm temperate seas
Synonyms, antonyms and the broader and narrower relations for jack come from Princeton University’s WordNet. Full sources and licences.