plugn.[Akin to D. plug, G. pflock, Dan. plk, 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.()Breech plug (Gun.), in breech-loading guns, the metal plug or cylinder which closes the aperture in the breech, through which the gun is loaded. -- Fire plug, a street hydrant to which hose may be attached. [U. S.] -- 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.()v. t. To stop with a plug; to make tight by stopping a hole.()