'barbarous' originates from Latin, specifically the word 'barbarus', which itself comes from Greek 'barbaros' meaning 'foreign' or 'non-Greek'.

'barbaros' in Greek passed into Latin as 'barbarus', then into Old French as 'barbarous', and was adopted into Middle English as 'barbarous', becoming the modern English 'barbarous'.

Initially it meant 'foreign' or 'strange' (i.e., someone who did not speak Greek), but over time it evolved to mean 'uncivilized' or 'savage', and later also 'cruel' or 'brutal'.