Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
Thestor, ŏris, m., = Θέστωρ, the father of the soothsayer Calchas, Hyg. Fab. 128.
Hence, Thestŏrĭdes, ae, m., the son of Thestor, i. e. Calchas, Ov. M. 12, 19; 12, 27; Stat. Achill. 1, 496.