Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
exsultābundus (exult-), a, um, adj. [exsulto], leaping for joy, exulting (postclass.): maesta ac lugentia castra velut exsultabundus intrare, Just. 18, 7, 10; so Sol. 5, 20.