Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
Sĕrēnātor, ōris, m. [sereno], he that makes fair weather, the clearer-up, an epithet of Jupiter, App. de Mundo, p. 75, 7; Inscr. Gud. p. 3, n. 8; p. 3, n. 9; p. 4, n. 1 sq.; cf. serenus.