Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
hĭlărĭtūdo, ĭnis, f. [hilaris], cheerfulness, merriment (ante-class. for the class. hilaritas): numquam ego te tristiorem Vidi esse: quid cedo tam abhorret hilaritudo? Plaut. Cist. 1, 1, 56: onera te hilaritudine, id. Mil. 3, 1, 83: ut in ocellis hilaritudo est! id. Rud. 2, 4, 8.