Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
2. Sīon, ōnis (or indecl.), m., f., or n., a hill of Jerusalem, and, by meton., Jerusalem, Prud. Ham. 459; Vulg. Matt. 21, 5: facta est deserta Sion, id. Isa. 64, 10.