Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
sŭb-ăgrestis, e, adj., somewhat rustic, rather boorish (Ciceronian): subagreste quiddam planeque subrusticum, Cic. Brut. 74, 259: consilium, id. Rep. 2, 7, 12: ingenium, Amm. 14, 11, 11.