Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
perfossor, ōris, m. [perfodio], a digger through, breaker through (ante- and post-class.): perfossor parietum, a house-breaker, Plaut. Ps. 4, 2, 23; App. Mag. p. 295, 16.