Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
laetĭtūdo, ĭnis, f. [laetus-facio], ante-class. for laetitia, joy: me excitasti ex luctu in laetitudinem, Att. ap. Non. 132, 12: affecti laetitudine, id. ib. 13 (Trag. Fragm. v. 61, 259 Rib.).