Source : Webster's Revised Unabridged Dictionary (1913)

Brat \Brat\ (br[a^]t), n. [OE. bratt coarse garnment, AS. bratt
   cloak, fr. the Celtic; cf. W. brat clout, rag, Gael. brat
   cloak, apron, rag, Ir. brat cloak; properly then, a child's
   bib or clout; hence, a child.]
   1. A coarse garment or cloak; also, coarse clothing, in
      general. [Obs.] --Chaucer.

   2. A coarse kind of apron for keeping the clothes clean; a
      bib. [Prov. Eng. & Scot.] --Wright.

   3. A child; an offspring; -- formerly used in a good sense,
      but now usually in a contemptuous sense. ``This brat is
      none of mine.'' --Shak. ``A beggar's brat.'' --Swift.

            O Israel! O household of the Lord! O Abraham's
            brats! O brood of blessed seed!       --Gascoigne.

   4. The young of an animal. [Obs.] --L'Estrange.

Brat \Brat\, n. (Mining)
   A thin bed of coal mixed with pyrites or carbonate of lime.

Source : WordNet®

brat
     n 1: a very troublesome child [syn: {terror}, {little terror}, {holy
          terror}]
     2: a small pork sausage [syn: {bratwurst}]