'deenergize' originates from the prefix 'de-' meaning 'remove' and the word 'energize' which comes from the Greek 'energein' meaning 'to be active'.

'energize' transformed from the Greek word 'energein' and eventually became the modern English word 'energize', with 'de-' added to form 'deenergize'.

Initially, it meant 'to remove energy', and this meaning has largely remained the same in modern usage.