'unfamiliar' originates from the prefix 'un-' meaning 'not' and the word 'familiar' from Latin 'familiaris', meaning 'of a household, domestic'.

'familiaris' transformed into the Old French word 'familier', and eventually became the modern English word 'familiar', with 'un-' added to form 'unfamiliar'.

Initially, 'familiar' meant 'of a household', but over time it evolved to mean 'well-known', and 'unfamiliar' as 'not well-known'.