Source : Webster's Revised Unabridged Dictionary (1913)

Three-quarter \Three"-quar`ter\, a. (Paint.)
   Measuring thirty inches by twenty-five; -- said of
   portraitures.

   {Three-quarter length}, a portrait showing the figure to the
      hips only.

Source : WordNet®

three-quarter
     adj : representing three quarters of something; "a
           three-quarter-length portrait"; "a three-quarter view"