Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
Thyestes, ae, m., = Θυέστης, son of Pelops and brother of Atreus, who set before him for food the flesh of his own son; he was the father of Ægisthus, Hyg. Fab. 88; Plaut. Rud. 2, 6, 25; Cic. Tusc. 3, 12, 26; Hor. A. P. 91; id. C. 1, 16, 17; Pers. 5, 8.
Hence,