Definition of midsummer men in US English:

midsummer men

noun

  • (Originally) a pair of orpine plants, symbolizing a young man and his sweetheart, which were set upright by girls on midsummer eve to prognosticate the course of their love; (in later use, also occasionally in singular as midsummer man) the plant orpine (Hylotelephium telephium) itself; the related plant roseroot, Sedum rosea.

Origin

Late 17th century; earliest use found in John Aubrey (1626–1697), antiquary and biographer.