From The Collaborative International Dictionary of English v.0.48 :
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.
[1913 Webster]
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.]
[1913 Webster]