Lewis & Short

Alcaeus, i, m., = Ἀλκαῖος, a renowned lyric poet of Mitylene, contemporary with Sappho, 610 B.C., inventor of the metre which bears his name, and which was imitated by the Latin poets, esp. by Horace; v. Hor. C. 2, 13, 27; 4, 9, 7; id. Ep. 1, 19, 29; 2, 2, 99; Ov. H. 15, 29 sq.; Quint. 10, 1, 63.
Hence, Alcăĭcus, a, um, adj., = Ἀλκαϊκός, of or pertaining to Alcœus: versus, the Alcaic verse; cf. Diom. 510 P.; Grotef. Gr. II. 107; Zumpt, Gr. § 866.