- pennyroyal oil - oil from European pennyroyal having a odor like mint; used chiefly in soaps
--1 is a kind of oil
--1 is a substance of pennyroyal, Mentha pulegium- pennyroyal oil, hedeoma oil - aromatic oil from American pennyroyal
--2 is a kind of oil
--2 is a substance of pennyroyal, American pennyroyal, Hedeoma pulegioides - pennyroyal oil, hedeoma oil - aromatic oil from American pennyroyal