Lewis & Short

Māmers, mertis, m., the Oscan name for Mars: Mamers Mamertis facit, id est lingua Osca Mars Martis, Paul. ex Fest. p. 131 Müll.; cf. id. s. v. Mamertini, p. 158 ib. The Sabines also gave to Mars the name of Mamers, acc. to Varr. L. L. 5, § 73 Müll.
Hence,

  1. A. Māmertīni, ōrum, m., the Mamertines.
    After the death of Agathocles of Syracuse, B. C. 289, the mercenary troops which he had collected from Umbria seized the city of Messana in Sicily, murdered the inhabitants, and made themselves masters of the vicinity. They called themselves Mamertines, from Mamers, Plin. 3, 8, 14, § 88; Cic. Verr. 2, 2, 5, § 13; id. Balb. 23, 52; Liv. 21, 22; 28, 28, 6.
  2. B. Māmertīnus, a, um, adj., of or belonging to the Mamertines, Mamertine: civitas, Cic. Verr. 2, 2, 5, § 13; 2, 3, 6, § 13; 2, 4, 10, § 22: vina, Plin. 14, 6, 8, § 66: amphora, Mart. 13, 117.