Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
rūpes, is (collat. form rūpa, ae, App. M. 6, p. 72 Hildebr. min.; cf. Gloss. Isid. p. 693),f. [rumpo], a rock: ex magnis rupibus nactus planitiem, Caes. B. C. 1, 70: cum (oppidum) ex omnibus in circuitu partibus altissimas rupes despectusque haberet, id. B. G. 2, 29; cf. Liv. 32, 4; and with this cf.: inter saxa rupesque, id. 21, 40: ex rupe Tarpeiā, id. 7, 10: Parnasia, Verg. E. 6, 29: aëria, id. G. 4, 508: ardua, Ov. F. 5, 293; id. P. 1, 8, 51: cavae, caverns, grottos, Verg. G. 3, 253; so, ima (Sibyllae), id. A. 3, 443.
Of a cliff, Verg. A. 10, 693; Luc. 5, 514; Val. Fl. 3, 108; 4, 637; cf.: personantibus et respondentibus inter se rupibus, Just. 24, 6, 8.