(Ἀτρείδης), a patronymic from Atreus, to designate his sons and descendants. When used in the singular, it commonly designates Agamemnon, but in the plural it signifies the two brothers, Agamemnon and Menelaus. (Hom. Il. 1.12, &c.; Hor. Carm. 2.4.7, &c.)
[L.S]A Dictionary of Greek and Roman biography and mythology
Smith, William
A Dictionary of Greek and Roman biography and mythology. William Smith, LLD, ed. 1890