Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
fosso, āvi, ātum, 1, v. freq. a. [fodio], to dig, pierce (ante-and post-class.): corpora telis, Enn. ap. Varr. L. L. 7, § 100 (Ann. v. 569 ed. Vahl.).
Hence,