Source : Webster's Revised Unabridged Dictionary (1913)

Semicircular \Sem`i*cir"cu*lar\, a.
   Having the form of half of a circle. --Addison.

   {Semicircular canals} (Anat.), certain canals of the inner
      ear. See under {Ear}.

Source : WordNet®

semicircular
     adj : curved into a half circle