Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
Massaesȳli (Masaes-), ōrum, m., = Μασσαισύλιοι, a people in Africa, Liv. 28, 17, 5; 29, 32; Plin. 5, 2, 1, § 17.
Hence, Massaesȳlia, ae, f., the country of the Massæsyli, Plin. 10, 8, 9, § 22.