Inhuman - Definition and More from the Free Merriam-Webster Dictionary
Definition of INHUMAN.
a: lacking pity, kindness, or mercy : savage <an inhuman tyrant>
b: cold, impersonal
The mass child murderer was thought to be inhuman.
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Something done without heart or mercy.
inhumane of inhuman? if inhumane than cruel, Without compassion for misery or suffering. if inhuman than not human, alien.
It can sometimes also refer to a feat literally not capable of a human, like inhuman speed or strength. Although generally if you call someone inhuman, you are saying that they are capable of behavioral acts that a normal human would not be, like killing a child or something else.