Source : Webster's Revised Unabridged Dictionary (1913)

Frown \Frown\, v. i. [imp. &, p. p. {Frowned}; p. pr. & vb. n.
   {Frowning}.] [OF. froignier, F. frogner, in se refrogner, se
   renfrogner, to knit the brow, to frown; perh. of Teutonic
   origin; cf. It. in frigno wrinkled, frowning, Prov. It.
   frignare to cringe the face, to make a wry face, dial. Sw.
   fryna to make a wry face,]
   1. To contract the brow in displeasure, severity, or
      sternness; to scowl; to put on a stern, grim, or surly
      look.

            The frowning wrinkle of her brow.     --Shak.

   2. To manifest displeasure or disapprobation; to look with
      disfavor or threateningly; to lower; as, polite society
      frowns upon rudeness.

            The sky doth frown and lower upon our army. --Shak.

Source : WordNet®

frowning
     adj : showing displeasure or anger