nefandous (adj.)

"not to be spoken of, abominable, very shocking to the general sense of justice or religion," 1630s, from Latin nefandus "unmentionable, impious, heinous," from ne-, negative particle (see un- (1)), + fandus "to be spoken," gerundive of fari "to speak," from PIE root *bha- (2) "to speak, tell, say."