Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
in-dēfīnītus, a, um, adj., indefinite (post-class.): sermo, Gell. 16, 4.
Hence, adv.: indēfīnītē, indefinitely: largiri, Gell. 2, 24, 7.