nefastus (ni-fas-t<<schwa>>s), n.[Latin ne “not” + fastus “lawful for public business”] Roman law. A day when it is unlawful to open the courts, administer justice, or hold public assemblies. • The priests in charge of supervising the laws and religious observances established an official calendar, on which certain days, marked “nefasti,” were to be devoted to religious or public ceremonies. — Also termed dies nefasti. Cf. dies fasti under DIES.

[Blacks Law 8th]