spark plug, sparking plug, plug -- (electrical device that fits into the cylinder head of an internal-combustion engine and ignites the gas by means of an electric spark)
plug, male plug -- (an electrical device with two or three pins that is inserted in a socket to make an electrical connection)
fireplug, fire hydrant, plug -- (an upright hydrant for drawing water to use in fighting a fire)
hack, jade, nag, plug -- (an old or over-worked horse)
Overview of verb plug
The verb plug has 6 senses
plug, stop up, secure -- (fill or close tightly with or as if with a plug; "plug the hole"; "stop up the leak")
plug, plug away -- (persist in working hard; "Students must plug away at this problem")
punch, plug -- (deliver a quick blow to; "he punched me in the stomach")
plug -- (make a plug for; praise the qualities or in order to sell or promote)
plug -- (insert a plug into; "plug the wall")
plug -- (insert as a plug; "She plugged a cork in the wine bottle")