Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
dēsŭētūdo, ĭnis, f. [desuesco], discontinuance of a practice or habit, disuse, desuetude: armorum, Liv. 1, 19: bellandi, Fronto, princ. hist. p. 3, 7: desuetudine tardi, Ov. M. 14, 436; so absol., id. Tr. 5, 7, 57; Dig. 1, 3, 32 al.