\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}.]