Pronunciation: (pen"ē-roi'ul),[key] —n. 1. an aromatic Old World plant, Mentha pulegium, of the mint family, having clusters of small purple flowers and yielding a pungent essential oil used medicinally and as an insect repellent.
2. Also called mock pennyroyal. a similar, related plant, Hedeoma pulegioides, of eastern North America, having bluish flowers growing from the leaf axils.
3. any of several other aromatic plants of the mint family.