maniatic
The only way you could have landed here is by reading ExR's translation of MDZS and ending up confused about this word and about not finding it anywhere. Let me tell you, this word probably doesn't exist. K probably wanted and adjective for the way a maniac acts. So, there you go, that's theoretically the definition.
"It was a maniatic way to kill others without dirtying his own hand, a merciless way to instead dirty the hand that fed him." -Chapter 40 of Mo Dao Zu Shi aka the Grandmaster of Demonic Cultivation