The Collaborative International Dictionary of English v.0.48:

Orillon \O*ril"lon\, n. [F., lit., a little ear, from oreille an
   ear, fr. L. oricula, auricula, dim. of auris an ear. See
   Ear.] (Fort.)
   A semicircular projection made at the shoulder of a bastion
   for the purpose of covering the retired flank, -- found in
   old fortresses.
   [1913 Webster]