Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
Mardi, ōrum, m., a plundering race dwelling in the highlands between Media, Susiana, and Persis, near the Hyrcanians, Plin. 6, 5, 5, § 16; 6, 16, 18, § 47; Tac. A. 14, 23; Curt. 4, 12, 7; 5, 6, 17; 6, 5, 11.
In sing.: natione Mardus, Curt. 3, 13, 2.