/pen'ee roy"euhl/ , 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.
[ 1520-30; PENNY + ROYAL; r. late ME puliol real poliol ( pulegiolum, dim. of pulegium pennyroyal) + real, earlier form of royal ]