Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
1. Moeris, ĭdis, m., = Μοῖρις, Mœris, a king of Egypt in the fifteenth century A. C., who caused the lake which bears his name to be excavated: Moeridis lacus, Plin. 5, 9, 9, § 50.
Hence,
2. Moeris, ĭdis, f., = Μοῖρις, the Lake Mœris, in Egypt, an artificial lake, fifty miles in width, between Memphis and Arsinoë, designed as a reservoir to hold the superfluous water of the Nile when overflowing, now Birket-Karum, Mel. 1, 9, 5 (ap. Plin. always Moeridis lacus).