Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
Ardŭenna, ae (Ardenna, Ven. Fort. Carm. 7, 4), f. [v. arduus; cf. Welsh ardh, to raise up], the forest-covered mountains in Gaul, now Ardennes, Caes. B. G. 5, 3; 6, 29 Herz.; Tac. A. 3, 42; cf. Mann. Gall. p. 203.