picket has 9 distinct synonyms spread across 3 of its 8 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 detachment of troops guarding an army from surprise attack
a protester posted by a labor organization outside a place of work
a vehicle performing sentinel duty
serve as pickets or post pickets
“picket a business to protest the layoffs”
fasten with a picket
“picket the goat”
Synonyms, antonyms and the broader and narrower relations for picket come from Princeton University’s WordNet. Full sources and licences.