Plug (?), n. [Akin to D. plug, G. pflock, Dan. plök, plug, Sw. plugg; cf. W. ploc.] 1. Any piece of wood, metal, or other substance used to stop or fill a hole; a stopple.
2. A flat oblong cake of pressed tobacco.
3. A high, tapering silk hat.
4. A worthless horse.
5. (Building) A block of wood let into a wall, to afford a hold for nails.
Fire plug, a street hydrant to which hose may be attached. — Hawse plug(Naut.), a plug to stop a hawse hole. — Plug and feather. (Stone Working) See Feather, n., 7. — Plug centerbit, a centerbit ending in a small cylinder instead of a point, so as to follow and enlarge a hole previously made, or to form a counterbore around it. — Plug rod(Steam Eng.), a rod attached to the beam for working the valves, as in the Cornish engine. — Plug valve(Mech.), a tapering valve, which turns in a case like the plug of a faucet.