Lewis & Short

Mĕton or Mĕto, ōnis, m., = Μέτων, a celebrated Athenian astronomer, who discovered the cycle of nineteen years, at the end of which the new and full moons again fall on the same days, Avien. Prognost. 48; Aus. Epis. 2, 12.
Hence Cicero says, jestingly, of a debtor named Meton, who promised to pay in a year’s time: quando iste Metonis annus veniet? Cic. Att. 12, 3, 2; cf. id. ib. 12, 51, 3.