Meaning

noun an annual horsemint of central and western United States and northern Mexico

noun tall erect perennial or annual having lanceolate leaves and heads of purple-spotted creamy flowers; many subspecies grown from eastern to southwestern United States and in Mexico

noun a coarse Old World wild water mint having long leaves and spikelike clusters of flowers; naturalized in the eastern United States

originFrom Middle English horsmynte, from Old English horsminte, equivalent to horse + mint.

Etymology from Wiktionary, CC BY-SA 3.0