noun An obstruction blocking a hole, pipe, etc. (somewhere in the pipes there is a plug of ice blocking the flow) A device for making an electrical connection, especially between an appliance and a power supply, consisting of an insulated casing with metal pins that fit into holes in an outlet. (the cable is fitted with a two-pin plug) A piece of publicity promoting a product, event, or establishment. A piece of tobacco cut from a larger cake for chewing. (they sold chewing tobacco in bars and plugs) A lure with one or more hooks attached. (Carrying plugs festooned with treble hooks is a price that is inevitably paid by the penitent plug fisherman.) short for fireplug A tired or old horse.