Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
ădăgĭo, ōnis, f., a rare form for adagium: “adagione: proverbio,” Gloss. Placid., Mai; Auct. ap. Varr. L. L. 7, § 31 Müll.; Aus. Monos. praef.