'undifferentiated' originates from the prefix 'un-' meaning 'not' and the word 'differentiated' which comes from Latin 'differentiare', meaning 'to make different'.

'differentiare' transformed into the English word 'differentiate', and eventually became 'undifferentiated' with the addition of the prefix 'un-'.

Initially, it meant 'not made different', and this meaning has largely remained the same in modern usage.