Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
Pȳthon, ōnis, m., = Πύθων, the serpent slain, according to the myth, near Delphi by Apollo, who was fabled to have been called Pythius in commemoration of this victory, Ov. M. 1, 438; 460; Claud. in Rufin. 1, 1.