Source : Webster's Revised Unabridged Dictionary (1913)

Petrous \Pe"trous\, a. [L. petrosus, fr. petra a stone.]
   1. Like stone; hard; stony; rocky; as, the petrous part of
      the temporal bone. --Hooper.

   2. (Anat.) Same as {Petrosal}.

Source : WordNet®

petrous
     adj : (of bone especially the temporal bone) resembling stone in
           hardness [syn: {stonelike}]