Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
insŭlānus, a, um, adj. [insula], of or belonging to an island: preces, offered by islanders, Sid. Ep. 9, 3; Pacat. Pan. Theod. 23, 3.
Hence, subst.: insŭlānus, i, m., an islander, Cic. N. D. 3, 18, 45.