Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
abscessĭo, ōnis, f. [abscedo], a going away, a separating: cum ad corpora tum accessio fieret, tum abscessio, i.e. diminution, * Cic. Univ. 12; Dict. Cret. B. Tr. 1, 5.