'unfriendly' originates from the prefix 'un-' meaning 'not' and the word 'friendly', which comes from Old English 'freondlic', where 'freond' meant 'friend'.

'freondlic' transformed into the Middle English word 'frendly', and eventually became the modern English word 'friendly', with 'un-' added to form 'unfriendly'.

Initially, 'friendly' meant 'like a friend', and 'unfriendly' evolved to mean 'not like a friend'.