Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
1. fĭber, fibri[ī], m., = castor, late Lat. beber [whence Germ. Biber; Eng. beaver], a beaver, Pontici, Plin. 8, 30, 47, § 109; 32, 3, 13, § 28; Plaut. Fragm. ap. Paul. ex Fest. p. 90 Müll.; Sil. 15, 490; Varr. L. L. 5, § 79 Müll.