Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
paenĭtūdo, ĭnis, f. [paeniteo], repentance (ante- and post-class. for paenitentia), Pac. ap. Non. 152, 30; 169, 25; Sid. Ep. 6, 9; Hier. Ep. 84; Ambros. Laps. Virg. 8, 33.