Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
com-pōtātĭo, ōnis, f., a drinking together, as transl. of the Gr. συμπόσιον (perh. only in Cic.), Cic. Sen. 13, 45; id. Fam. 9, 24, 3.