Source : Webster's Revised Unabridged Dictionary (1913)

Stag \Stag\, n. [Icel. steggr the male of several animals; or a
   doubtful AS. stagga. Cf. {Steg}.]
   1. (Zo["o]l.)
      (a) The adult male of the red deer ({Cervus elaphus}), a
          large European species closely related to the American
          elk, or wapiti.
      (b) The male of certain other species of large deer.

   2. A colt, or filly; also, a romping girl. [Prov. Eng.]

   3. A castrated bull; -- called also {bull stag}, and {bull
      seg}. See the Note under {Ox}.

   4. (Stock Exchange)
      (a) An outside irregular dealer in stocks, who is not a
          member of the exchange. [Cant]
      (b) One who applies for the allotment of shares in new
          projects, with a view to sell immediately at a
          premium, and not to hold the stock. [Cant]

   5. (Zo["o]l.) The European wren. [Prov. Eng.]

   {Stag beetle} (Zo["o]l.), any one of numerous species of
      lamellicorn beetles belonging to {Lucanus} and allied
      genera, especially {L. cervus} of Europe and {L. dama} of
      the United States. The mandibles are large and branched,
      or forked, whence the name. The lava feeds on the rotten
      wood of dead trees. Called also {horned bug}, and {horse
      beetle}.

   {Stag dance}, a dance by men only. [slang, U.S.]

   {Stag hog} (Zo["o]l.), the babiroussa.

   {Stag-horn coral} (Zo["o]l.), any one of several species of
      large branching corals of the genus {Madrepora}, which
      somewhat resemble the antlers of the stag, especially
      {Madrepora cervicornis}, and {M. palmata}, of Florida and
      the West Indies.

   {Stag-horn fern} (Bot.), an Australian and West African fern
      ({Platycerium alcicorne}) having the large fronds branched
      like a stag's horns; also, any species of the same genus.
      

   {Stag-horn sumac} (Bot.), a common American shrub ({Rhus
      typhina}) having densely velvety branchlets. See {Sumac}.
      

   {Stag party}, a party consisting of men only. [Slang, U. S.]
      

   {Stag tick} (Zo["o]l.), a parasitic dipterous insect of the
      family {Hippoboscid[ae]}, which lives upon the stag and in
      usually wingless. The same species lives also upon the
      European grouse, but in that case has wings.

Source : WordNet®

stag beetle
     n : a kind of lamellicorn beetle; the male has branched
         mandibles resembling antlers