'unabbreviated' originates from the prefix 'un-' meaning 'not' and the word 'abbreviated' from Latin 'abbreviare', where 'ad-' meant 'to' and 'breviare' meant 'shorten'.

'abbreviare' transformed into the Old French word 'abregier', and eventually became the modern English word 'abbreviate', with 'un-' added to form 'unabbreviated'.

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