The Collaborative International Dictionary of English v.0.48:

Omahas \O"ma*has"\, prop. n. pl.; sing. Omaha. (Ethnol.)
   A tribe of Indians who inhabited the south side of the
   Missouri River. They are now partly civilized and occupy a
   reservation in Nebraska.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Maha \Ma"ha\, prop. n. (Ethnol.)
   A member of the Siouan people formerly living in the Missouri
   river valley in Northeastern Nebraska; called also Omaha.
   [WordNet 1.5] Mahabarata

WordNet (r) 3.0 (2006):

Omaha
    n 1: a member of the Siouan people formerly living in the
         Missouri river valley in northeastern Nebraska [syn:
         Omaha, Maha]
    2: largest city in Nebraska; located in eastern Nebraska on the
       Missouri river; a major transportation center of the Midwest
    3: the Dhegiha dialect spoken by the Omaha
    4: thoroughbred that won the triple crown in 1935