Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
sĭlesco, ĕre, v. inch. n. [sileo], to become still, silent, calm, or quiet (rare; not in Cic.; syn. obmutesco): dum hae silescunt turbae, Ter. Ad. 5, 2, 10: deum domus alta silescit, Verg. A. 10, 101: caeli furor aequinoctialis Zephyri silescit auris, Cat. 46, 3: venti silescunt, Ov. Tr. 2, 151.