Definition of bastard pennyroyal in English:

bastard pennyroyal

noun

US
  • Any of several aromatic North American plants of the genus Trichostema (family Lamiaceae); especially T. dichotomum, which has hairy branching stems, oval leaves, and bright blue flowers with a prominent lower lip and long curled stamens.

Origin

Early 19th century; earliest use found in William Barton (1786–1856).