petr- combining form orpetri-orpetro- Etymology: Middle French petr-, petri- & Latin petr- & New Latin petro-, from Greek petr-, petro-, from petros stone & petra rock 1. a.: stone : rock < petrescent > < Petricola > < petrogenesis > b.: petroleum < petroporphyrins > 2.: of or relating to the petrous portion of the temporal bone and < petrohyoid >