Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
indignābundus, a, um, adj. [indignor], full of indignation, enraged, indignant (not ante-Aug.): illa muliebriter indignabunda, Liv. 38, 57, 7; with clamitans, Suet. Aug. 40: animo irritato, indignabundus, Gell. 19, 9, 8.