pennyroyal Meaning, Definition & Usage

  1. noun Eurasian perennial mint have small lilac-blue flowers and ovate leaves; yields an aromatic oil
    Mentha pulegium.
  2. noun erect hairy branching American herb having purple-blue flowers; yields an essential oil used as an insect repellent and sometimes in folk medicine
    American pennyroyal; Hedeoma pulegioides.

WordNet

Pen`ny*roy"al noun
Etymology
A corruption of OE. puliall royal. OE. puliall is ultimately derived fr. L. puleium, or pulegium regium (so called as being good against fleas), fr. pulex a flea; and royal is a translation of L. regium, in puleium regium.
Definitions
  1. (Bot.) An aromatic herb (Mentha Pulegium) of Europe; also, a North American plant (Hedeoma pulegioides) resembling it in flavor.

Webster 1913