Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
trīcēsĭmus (less freq. trīgēsĭmus, Mart. 1, 16, 3; 10, 103, 7; Just. 12, 15), a, um, num. ord. adj. [triginta], the thirtieth: idem tricesimo post die feci, Cic. Fam. 12, 2, 1: tertius et tricesimus annus, id. Sen. 6, 19: sexto tricesimo anno post, id. Off. 2, 8, 29: legio quinta tricesima, Galb. ap. Cic. Fam. 10, 30, 1: tricesimo sexto anno, Liv. 3, 30, 7: tricesimum annum agens, id. 40, 6, 4: tricesimo die, Curt. 5, 6, 19: tricesima sabbata, Hor. S. 1, 9, 69: bis trigesimus consul instat, Mart. 1, 16, 3.
Hence, subst.: Trīcēsĭmae, ārum, f., the name of a town in Gallia Belgica on the Rhine, Amm. 18, 2, 4.
trīgēsĭmus, a, um, v. tricesimus.