Barbaric means cruel and uncivilised beyond excuse. A word used about acts nobody wants to defend.
It is worth handling carefully, since it comes from the Greek barbaros, meaning somebody who does not speak Greek, and it has spent most of its history dismissing whole peoples as savages, which is exactly how a great deal of conquest was justified. Modern use is nearly always about a specific act rather than a people. Barbarous is the near synonym and barbarity is the noun.
1adjectivebarbaricSavagely cruel and uncivilised.
“The treatment of the prisoners was barbaric.”
Also accepted in games: brutal, savage
Ancient Greek
βαρβαρικός — barbaric, savage, fierce
Latin
barbaricus
Old French
barbarique — barbarous
Middle English
barbarik
English, today
barbaric
Inherited from Middle English barbarik, from Old French barbarique (“barbarous”), from Latin barbaricus, from Ancient Greek βαρβαρικός (“barbaric, savage, fierce”), from βάρβαρος + -ικός. See βάρβαρος for more.
Etymology from Wiktionary, CC BY-SA