Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
ob-sīdo, ĕre, v. a., to beset, invest, besiege, blockade (mostly poet.): ne auriculam obsidat caries, ne vermiculique, Lucil. ap. Non. 21, 25: vias oculorum, Lucr. 4, 351: certas partes, id. 4, 1092: pontem, Sall. C. 45, 2 Kritz N. cr.: portas, Verg. A. 9, 159: Italos fines, to occupy, take possession of, id. ib. 7, 334: praedator cupit immensos obsidere campos, Tib. 2, 3, 41: Troica moenia, Cat. 64, 345.