bestial

/ˈbɛstʃəl/

/ˈbistjəl/

Bestial sounds like beast, and that is precisely what it means, "beast-like." When a human acts like an animal, their behavior is called bestial.

Bestial is often used to describe behavior that is primitive or uncivilized. If someone living on a desert island took to grunting and crawling on all fours searching for bugs in dirt, you could say she had descended to the bestial.

Definitions of bestial

1. adjective

   resembling a beast; showing lack of human sensibility
   “a bestial nature”

   “bestial treatment of prisoners”

   synonyms: beastly, brutal, brute, brutish

   inhumane

   reflecting lack of pity or compassion