The Collaborative International Dictionary of English v.0.48:

Oto- \O"to-\ [Gr. o'y^s, 'wto`s, the ear.]
   A combining form denoting relation to the ear, or situation
   near the ear or in the ear.
   [1913 Webster]

WordNet (r) 3.0 (2006):

Oto
    n 1: a member of the Siouan people inhabiting the valleys of the
         Platte and Missouri rivers in Nebraska [syn: Oto, Otoe]
    2: a dialect of the Chiwere language spoken by the Oto [syn:
       Oto, Otoe]

U.S. Gazetteer Places (2000):

Oto, IA -- U.S. city in Iowa
   Population (2000):    145
   Housing Units (2000): 67
   Land area (2000):     0.262364 sq. miles (0.679520 sq. km)
   Water area (2000):    0.000000 sq. miles (0.000000 sq. km)
   Total area (2000):    0.262364 sq. miles (0.679520 sq. km)
   FIPS code:            60240
   Located within:       Iowa (IA), FIPS 19
   Location:             42.283676 N, 95.894047 W
   ZIP Codes (1990):     51044
   Note: some ZIP codes may be omitted esp. for suburbs.
   Headwords:
    Oto, IA
    Oto