Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
Sēstos (-us), i, f., = Σηστός, a city in Thrace, on the Hellespont, opposite Abydos, the residence of Hero: Leandri amore pernobilis, Mel. 2, 2, 7; Plin. 4, 11, 18, § 49; Liv. 32, 33; 37, 9; Ov. H. 18, 127; Luc. 2, 674; 6, 55.
Hence,