Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
vīpĕrĕus, a, um, adj. [vipera], of a viper, serpent, or snake: crinis, Verg. A. 6, 281: dentes, Ov. M. 4, 573: fauces, id. ib. 7, 203: carnes, id. ib. 2, 769: venenum, Luc. 9, 635; cf. cruor, Ov. P. 4, 7, 36: genus, Verg. A. 7, 753: monstrum, i. e. the serpent-haired head of Medusa, Ov. M. 4, 615; cf. sorores, i. e. the Furies, id. ib. 6, 662: pennae, i. e. winged serpents, id. ib. 7, 391: genus fratrum, sprung from the dragon’s teeth of Cadmus, Sen. Oedip. 597: manus, with serpent fingers, id. Herc. Oet. 169: anima, i. e. poisonous breath, Verg. A. 7, 351.