Lewis & Short

Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.

Mărăthēnus, a, um, v. Marathos, II.

Mărăthos or -us, i, f., = Μάραθος, an ancient Phœnician city, opposite the island of Arados, near the modern Ainel-Hye, Mel. 1, 12, 3; Plin. 5, 20, 17, § 78; Curt. 4, 1, 6.
Hence, Mărăthēnus, a, um, adj., of or from Marathos, Marathene: Menelaüs, a rhetorician from Marathos, Cic. Brut. 26, 100 Meyer.