Source : Webster's Revised Unabridged Dictionary (1913)

Pennyroyal \Pen`ny*roy"al\, n. [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.] (Bot.)
   An aromatic herb ({Mentha Pulegium}) of Europe; also, a North
   American plant ({Hedeoma pulegioides}) resembling it in
   flavor.

   {Bastard pennyroyal} (Bot.) See {Blue curls}, under {Blue}.

Source : WordNet®

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