Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
excĭdĭo, ōnis, f. [exscindo, v. 1. excidium], a destroying, destruction: oppidi, Plaut. Curc. 4, 3, 2; cf.: excidionem urbis a caedendo dictam manifestum est, Paul. ex Fest. p. 80, 9 Müll.