'barbarious' originates from Latin, ultimately from the word 'barbarus', where 'barbar-' meant 'foreign' or 'strange' (used by Greeks and Romans for non-Greek/non-Roman peoples).

'barbarious' came into English via Old French/Medieval Latin forms (e.g. Old French 'barbarous', Medieval Latin 'barbaricus') and appeared in Middle English alongside forms like 'barbarous' and 'barbarious'.

Initially it signified 'foreign' or 'strange' (as in 'non-Greek/non-Roman'); over time the sense shifted toward 'savage' or 'cruel', which is the primary meaning in later English.