Source : Webster's Revised Unabridged Dictionary (1913)

Oh \Oh\, interj. [See O, interj.]
   An exclamation expressing various emotions, according to the
   tone and manner, especially surprise, pain, sorrow, anxiety,
   or a wish. See the Note under O.

Source : WordNet®

OH
     n : a midwestern state in north central United States in the
         Great Lakes region [syn: {Ohio}, {Buckeye State}]