Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
‡ sexātrūs, uum, f. [sex], the sixth day after the Ides: sexatrus ab Tusculanis post diem sextum Idus vocatur (dies), Varr. L. L. 6, § 14 Müll.; cf. Fest. s. v. Quinquatrus, p. 254 ib.