Inhuman, cruel (6)
I believe the answer is:
brutal
I believe this clue is a double definition.
'inhuman' is the first definition.
(I've seen this before)
'cruel' is the second definition.
(I know that cruel can be written as brutal)
(Other definitions for brutal that I've seen before include "Harsh, merciless" , "Cruel, animal-like" , "Very cruel and beastly" , "Disposed to inflict pain" , "Callous" .)