Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
Ēĕtĭon, ōnis, m., = Ἠετίων, the father of Andromache, and king of Thebe, in Cilicia, Ov. Tr. 5, 5, 44; id. F. 4, 280.
Hence, Ēĕtĭōnēus, a, um, pertaining to Eëtion: Thebae, Ov. M. 12, 110.