Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
perfunctĭo, ōnis, f. [perfungor], a performing, discharging of an office (class.): honorum, Cic. de Or. 3, 2, 7: laborum, an undergoing, enduring (along with perpessio dolorum), id. Fin. 1, 15, 49.
Of things: annua fertur ei totius spatii esse perfunctio, Ambros. Hexaëm. 4, 5, 24.