plug has 22 distinct synonyms spread across 10 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.
electrical device that fits into the cylinder head of an internal-combustion engine and ignites the gas by means of an electric spark
an electrical device with two or three pins that is inserted in a socket to make an electrical connection
an upright hydrant for drawing water to use in fighting a fire
Synonyms, antonyms and the broader and narrower relations for plug come from Princeton University’s WordNet. Full sources and licences.
make a plug for; praise the qualities or in order to sell or promote
replace the center of a coin with a baser metal
“plug a nickle”
insert as a plug
“She plugged a cork in the wine bottle”