Definitions of plug:

• noun:   blockage consisting of an object designed to fill a hole tightly
• noun:   an electrical device with two or three pins that is inserted in a socket to make an electrical connection
• noun:   an upright hydrant for drawing water to use in fighting a fire
• noun:   electrical device that fits into the cylinder head of an internal-combustion engine and ignites the gas by means of an electric spark
• noun:   an old or over-worked horse
• noun:   blatant or sensational promotion
• noun:   a wad of something chewable as tobacco
• verb:   persist in working hard

  Example: "Students must plug away at this problem"

• verb:   make a plug for; praise the qualities or in order to sell or promote
• verb:   fill or close tightly with or as if with a plug

  Example: "Plug the hole"

• verb:   deliver a quick blow to