Source : Webster's Revised Unabridged Dictionary (1913)

Hound's-tongue \Hound's"-tongue`\, n. [AS. hundes tunge.] (Bot.)
   A biennial weed ({Cynoglossum officinale}), with soft
   tongue-shaped leaves, and an offensive odor. It bears nutlets
   covered with barbed or hooked prickles. Called also
   {dog's-tongue}.

Source : WordNet®

hound's-tongue
     n 1: perennial shrub of North America having coarse tongue-shaped
          leaves and pale-blue to purple flowers [syn: {Cynoglossum
          virginaticum}]
     2: biennial shrub of Europe and western Asia having coarse
        tongue-shaped leaves and dark reddish-purple flowers [syn:
         {Cynoglossum officinale}]