Source : Webster's Revised Unabridged Dictionary (1913)

Amish \Am"ish\, n. pl. [Written also {Omish}.] (Eccl. Hist.)
   The Amish Mennonites.

Amish \Am"ish\, a. [Written also {Omish}.] (Eccl. Hist.)
   Of, pertaining to, or designating, the followers of Jacob
   Amman, a strict Mennonite of the 17th century, who even
   proscribed the use of buttons and shaving as ``worldly
   conformity''. There are several branches of Amish Mennonites
   in the United States.

Source : WordNet®

Amish
     n : an American follower of the Mennonite religion