/ˈbestiəl/
[adjective] Relating to or behaving like a wild animal; cruel, violent, or without human feeling. It describes actions or behaviour that seem completely inhuman or savage.
The word 'bestial' carries within it the entire Latin zoo — 'bestia' simply meant any wild, dangerous animal.
The story of 'bestial' begins in ancient Rome with the Latin word 'bestia', meaning a wild or dangerous animal — the kind of creature that prowled outside the edges of civilised life. Romans used 'bestia' specifically to contrast the untamed world of nature with the ordered world of human society. The word carried a sense of threat and otherness, and from it came 'bestialis', the Latin adjective meaning 'of or relating to a beast'. This is the direct ancestor of the English word we use today.
The word travelled through Old French as 'bestial' before arriving in Middle English in the 14th century, largely unchanged in form but increasingly rich in moral meaning. In medieval Christian thinking, the distinction between humans and animals was deeply important — humans had reason and a soul, while animals were driven purely by instinct and appetite. To call someone or something 'bestial' was therefore not just a description but a condemnation, placing a person morally below the level that God intended for humankind.
The same Latin root 'bestia' gave English several other words through different paths. 'Beast' itself came directly from Old French 'beste', which descended from 'bestia'. 'Beastly' followed much later as an English formation built on 'beast'. Meanwhile, the more exotic-sounding 'bestiary' — the name for those illustrated medieval books cataloguing real and mythical animals — also comes straight from 'bestia' via Medieval Latin 'bestiarium', meaning a collection or place of wild animals.
Interestingly, 'bestia' may have very deep roots indeed. Some linguists connect it to an older Proto-Indo-European root related to blowing or breathing — the idea being that what most essentially defined an animal was simply that it breathed and moved with life. Under this theory, the Latin 'bestia' is a creature defined by its raw, breathing vitality, untouched by reason. This theory is debated, but it adds a poetic dimension to the word: the beast is, at its core, a breathing thing with no inner moral life.
Over the centuries, 'bestial' has been used consistently to describe warfare, cruelty, lust, and oppression of the worst kind. Writers reaching for the most extreme condemnation of human behaviour have reliably turned to this word. What makes it so effective is exactly that medieval logic still alive inside it — the idea that there is a line between the human and the animal, and that crossing it in one's behaviour is not just wrong but a kind of self-degradation, a falling away from what we are supposed to be. The word does not merely describe violence; it classifies it as a betrayal of humanity itself.