Source : Webster's Revised Unabridged Dictionary (1913)

Senecas \Sen"e*cas\, n. pl.; sing. {Seneca}. (Ethnol.)
   A tribe of Indians who formerly inhabited a part of Western
   New York. This tribe was the most numerous and most warlike
   of the Five Nations.

   {Seneca grass}(Bot.), holy grass. See under {Holy}.

   {Seneca eil}, petroleum or naphtha.

   {Seneca root}, or {Seneca snakeroot} (Bot.), the rootstock of
      an American species of milkworth ({Polygala Senega})
      having an aromatic but bitter taste. It is often used
      medicinally as an expectorant and diuretic, and, in large
      doses, as an emetic and cathartic. [Written also {Senega
      root}, and {Seneka root}.]

Source : WordNet®

senega root
     n : eastern North American plant having a terminal cluster of
         small white flowers and medicinal roots [syn: {Seneca
         snakeroot}, {Seneka snakeroot}, {senga root}, {senega
         snakeroot}, {Polygala senega}]