dog's mercury

 

noun

  • a Eurasian plant of the spurge family, with hairy stems and small green flowers, found as a dominant plant of old woodland.
    • Mercurialis perennis, family Euphorbiaceae

Origin:

late 16th century: translating modern Latin Mercurialis canina (former taxonomic name); the plant is poisonous and is contrasted with Mercurialis annua 'annual mercury', useful in medicine