Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
1. sil, silis, n., a kind of yellowish earth, yellow ochre, Plin. 33, 12, 56, § 158; Vitr. 7, 11; Veg. 5, 26; 5, 39; 6, 28 fin.; Aus. Idyll. 12, Gram. 8.
2. sil or sili, = seselis.