Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
Cūpra, ae, f., the name of two cities in Picenum, Mel. 2, 4, 6; Plin. 3, 13, 18, § 111; Sil. 8, 434.
Hence, Cūprenses, ium, m., their inhabitants, Plin. l. l.