Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
per-bŏnus, a, um, adj., very good: prandium, Plaut. Most. 3, 2, 3: eam sei curabeis, perbona’st, id. Merc. 3, 1, 28: ager, Cic. Fl. 29, 71: toreumata, id. Verr. 2, 4, 18, § 38: perbono loco res erat, id. Att. 6, 1, 3.