Source : Webster's Revised Unabridged Dictionary (1913)

Plug \Plug\, n.

   {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. Plug board \Plug board\
   (Elec.)
   A switchboard in which connections are made by means of
   plugs.

Plug \Plug\, v. t. [imp. & p. p. {Plugged}; p. pr. & vb. n.
   {Plugging}.]
   To stop with a plug; to make tight by stopping a hole.

Plug \Plug\, n. [Akin to D. plug, G. pflock, Dan. pl["o]k, 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. [U. S.]

   3. A high, tapering silk hat. [Slang, U.S.]

   4. A worthless horse. [Slang, U.S.]

   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.
      [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.

Source : WordNet®

plug
     n 1: blockage consisting of an object designed to fill a hole
          tightly [syn: {stopper}, {stopple}]
     2: a wad of something chewable as tobacco [syn: {chew}, {chaw},
         {cud}, {quid}, {wad}]
     3: blatant or sensational promotion [syn: {ballyhoo}, {hoopla},
         {hype}]
     4: electrical device that fits into the cylinder head of an
        internal-combustion engine and ignites the gas by means of
        an electric spark [syn: {spark plug}, {sparking plug}]
     5: an electrical device with two or three pins that is inserted
        in a socket to make an electrical connection [syn: {male
        plug}]
     6: an upright hydrant for drawing water to use in fighting a
        fire [syn: {fireplug}, {fire hydrant}]
     7: an old or over-worked horse [syn: {hack}, {jade}, {nag}]
     [also: {plugging}, {plugged}]

plug
     v 1: fill or close tightly with or as if with a plug; "plug the
          hole"; "stop up the leak" [syn: {stop up}, {secure}]
     2: persist in working hard; "Students must plug away at this
        problem" [syn: {plug away}]
     3: deliver a quick blow to; "he punched me in the stomach"
        [syn: {punch}]
     4: make a plug for; praise the qualities or in order to sell or
        promote
     [also: {plugging}, {plugged}]