Plug  —n. 1 piece of solid material fitting tightly into a hole, used to fill a gap or cavity or act as a wedge or stopper. 2 a device of metal pins in an insulated casing, fitting into holes in a socket for making an electrical connection. B colloq. Electric socket. 3 = *spark-plug. 4 colloq. Piece of free publicity for an idea, product, etc. 5 cake or stick of tobacco; piece of this for chewing. —v. (-gg-) 1 (often foll. By up) stop (a hole etc.) With a plug. 2 slang shoot or hit (a person etc.). 3 colloq. Seek to popularize (an idea, product, etc.) By constant recommendation. 4 colloq. (foll. By away (at)) work steadily (at).  plug in connect electrically by inserting a plug into a socket. [low german or dutch]