Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
octōgēsĭmus, a, um, num. ord. adj. [octoginta], the eightieth: quartum annum ago et octogesimum, Cic. Sen. 10, 32; 2, 4: solstitia, Juv. 4, 92.