nĕ-fas (noun N) :
* Indecl., something contrary to divine law, sinful, unlawful, execrable, abominable, criminal; an impious or wicked deed, a sin, a crime (cf.: scelus, flagitium, peccatum).
* Lit.: quicquid non licet, nefas putare debemus,Cic. Par. 3, 2. 25; cf.: officia tua mihi nefas est oblivisci,id. Fam. 15, 21, 5: Mercurius, quem Aegyptii nefas habent nominare,id. N. D. 3, 22, 56: nefas est dictu, miseram fuisse talem senectutem, id. Sen. 5, 13: eum, cui nihil umquam nefas fuit,id. Mil. 27, 73: quibus nefas est ... deserere patronos,Caes. B. G. 7, 40: corpora viva nefas Stygiā vectare carinā,Verg. A. 6, 391: fas atque nefas,right and wrong,id. G. 1, 505; Hor. Epod. 5, 87; cf. id. C. 1, 18, 10; Ov. M. 6, 585: per omne fas ac nefas,in every way,Liv. 6, 14, 10: nefas triste piare,Verg. A. 2, 184: illa dolos dirumque nefas in pectore versat, Certa mori,id. ib. 4, 563: lex maculosum edomuit nefas,i. e. adultery,Hor. C. 4, 5, 22: in omne nefas se parare,Ov. M. 6, 613: summum crede nefas animam praeferre pudori,Juv. 8, 83: belli,civil war,Luc. 2, 507; cf.: fugiens civile nefas,id. 7, 432: magnum nefas contrahere,Just. 24, 3: facere nefas,Vulg. Deut. 22, 21: operari,ib. Lev. 20, 13.—Poet., of a wicked person, a wretch, monster: exstinxisse nefas tamen ... Laudabor (i. e. Helen, as the destroyer of Troy),Verg. A. 2, 585.—Also inserted as an interjection, O horrid! shocking! dreadful! quātenus, heu nefas! virtutem incolumem odimus, Hor. C. 3, 24, 30; cf.: heu nefas, heu!id. ib. 4, 6, 17: quosne, nefas! omnes infandā in morte reliqui?Verg. A. 10, 673: sequiturque, nefas! Aegyptia conjux,id. ib. 8, 688: Lavinia virgo Visa, nefas! longis comprendere crinibus ignem,O horrible!id. ib. 7, 73.—Esp.: est nefas,it is forbidden, contrary to law,Varr. L. L. 6, 4.
* Poet., transf.
* A horrible or monstrous thing: Eumenides Stygiumque nefas,Luc. 6, 695; 1, 626: infernum,id. 7, 170; Stat. Th. 6, 942.
* Impossible: levius fit patientiā Quicquid corrigere est nefas, an impossibility (= ἀθέμιτον, ἀδύνατον), Hor. C. 1, 24, 20.

s. TLL