'unreactive' originates from the prefix 'un-' meaning 'not' and the word 'reactive', which comes from the Latin 'reactivus', where 're-' meant 'again' and 'activus' meant 'active'.

'reactivus' transformed into the English word 'reactive', and with the addition of the prefix 'un-', it became 'unreactive'.

Initially, 'reactive' meant 'capable of reacting', and with the prefix 'un-', it evolved to mean 'not capable of reacting'.