The Collaborative International Dictionary of English v.0.48:

Semicircular \Sem`i*cir"cu*lar\, a.
   Having the form of half of a circle. --Addison.
   [1913 Webster]

   Semicircular canals (Anat.), certain canals of the inner
      ear. See under Ear.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

curved \curved\ adj.
   1. not straight; having or marked by curves. Opposite of
      straight.

   Note: [Narrower terms: arced, arched, arching, arciform,
         arcuate, bowed; falcate, sickle-shaped; flexuous;
         incurvate, incurved: recurved, recurvate;
         semicircular: serpentine, snaky: sinuate, sinuous,
         wavy: sinusoidal]

   Syn: curving.
        [WordNet 1.5]

   2. (Botany) curved with the micropyle near the base almost
      touching its stalk; -- of a plant ovule. Opposite of
      orthotropous.

   Syn: campylotropous.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

semicircular
    adj 1: curved into a half circle

Moby Thesaurus II by Grady Ward, 1.0:

26 Moby Thesaurus words for "semicircular":
   Cynthian, S-shaped, bicorn, corniform, crescent, crescent-shaped,
   crescentic, crescentiform, crescentlike, falcate, falciform,
   horn-shaped, horned, lunar, lunate, luniform, lunular, menisciform,
   meniscoid, moon-shaped, moonlike, semilunar, sickle-like,
   sickle-shaped, sigmoid, two-horned