Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
Ŏăsis, is, f., = Ὄασις [orig. a Coptic word], an inhabited spot, a fertile piece of land in the Libyan desert, an oasis; esp. the great oasis in Upper Egypt, to which criminals were banished by the emperors, Cod. Just. 9, 47, 26; Dig. 48, 22, 7, § 5.
Hence,