Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
undētrīcēsĭmus or undētrīgē-sĭmus, a, um, num. adj. [unus-desexaginta], the twentyninth: dies, Liv. 25, 36, 14: in commentariorum undetricesimo, Gell. 10, 5, 1.