'unilluminated' originates from the prefix 'un-' meaning 'not' and the word 'illuminate' from Latin 'illuminare', where 'in-' meant 'in' and 'luminare' meant 'to light up'.

'illuminare' transformed into the Old French word 'illuminer', and eventually became the modern English word 'illuminate'. The prefix 'un-' was added to form 'unilluminated'.

Initially, 'illuminate' meant 'to light up or make clear', and 'unilluminated' has retained the meaning of 'not being lit up'.