Source : Webster's Revised Unabridged Dictionary (1913)

Ramus \Ra"mus\, n.; pl. {Rami}. (Nat. Hist.)
   A branch; a projecting part or prominent process; a
   ramification.

Source : WordNet®

ramus
     n : the posterior part of the mandible that is more or less
         vertical
     [also: {rami} (pl)]