Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
Aetnensis, e, adj. [Aetna], pertaining to the town of Ætna (at the foot of Mt. Ætna, v. Strab. 6, p. 185): ager, Cic. Verr. 2, 3, 18.
Hence, Aetnenses, ĭum, m., the inhabitants of Ætna, Plin. 3, 8, 14, § 91.