Source : Webster's Revised Unabridged Dictionary (1913)

Bug \Bug\, n. [OE. bugge, fr. W. bwg, bwgan, hobgoblin,
   scarecrow, bugbear. Cf. {Bogey}, {Boggle}.]
   1. A bugbear; anything which terrifies. [Obs.]

            Sir, spare your threats: The bug which you would
            fright me with I seek.                --Shak.

   2. (Zo["o]l.) A general name applied to various insects
      belonging to the Hemiptera; as, the squash bug; the chinch
      bug, etc.

   3. (Zo["o]l.) An insect of the genus {Cimex}, especially the
      bedbug ({C. lectularius}). See {Bedbug}.

   4. (Zo["o]l.) One of various species of Coleoptera; as, the
      ladybug; potato bug, etc.; loosely, any beetle.

   5. (Zo["o]l.) One of certain kinds of Crustacea; as, the sow
      bug; pill bug; bait bug; salve bug, etc.

   Note: According to present popular usage in England, and
         among housekeepers in America, bug, when not joined
         with some qualifying word, is used specifically for
         bedbug. As a general term it is used very loosely in
         America, and was formerly used still more loosely in
         England. ``God's rare workmanship in the ant, the
         poorest bug that creeps.'' --Rogers (--Naaman). ``This
         bug with gilded wings.'' --Pope.

   {Bait bug}. See under {Bait}.

   {Bug word}, swaggering or threatening language. [Obs.]
      --Beau. & Fl.