ˈpe.trəs, ˈpē.- adjective
Etymology: Middle French petreux, from Latin petrosus rocky, from petra rock (from Greek) + -osus -ose
: resembling stone especially in hardness : rocky ; specifically : of, relating to, or constituting the exceptionally hard and dense portion of the temporal bone of man that contains the internal auditory organs, corresponds chiefly to the periotic bones of many vertebrates, and is a pyramidal process wedged in at the base of the skull between the sphenoid and occipital bones with its lower half exposed on the surface of the skull and pierced by the external auditory meatus