Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
Oxos or -us, i, m., = Ὦξος, the Oxus, a river in Asia, which rises on the borders of Hyrcania and Sogdiana, and flows into the Caspian Sea, now the Amu or Jihon, Mel. 3, 5, 6; Plin. 6, 16, 18, § 48; Curt. 7, 4, 5.