2. A surname of Zeus, under which he was worshipped at Sparta. (Lycophr. 335, with the Schol.; Eustath. ad Il. 2.25.) Eustathius thinks that the god derived this name from the resemblance between him and Agamemnon; while others believe that it is a mere epithet signifying the Eternal, from ἀγὰν and μένων.
[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