Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
serpyllum or serpillum (Varr. L. L. 5, § 103 Müll. p. 30 Bip.; and in MSS. of Cato, R. R. also serpull-; v. the letter U), i, n. [sibilated from ἕρπυλλον], thyme, wildthyme: Thymus serpyllum, Linn.; Cato, R. R. 73; Varr. R. R. 1, 35, 2; Col. 11, 3, 39; Plin. 20, 22, 90, § 245; Pall. Mart. 9, 17; Verg. E. 2, 11; id. G. 4, 31 al.