're-activator' originates from the Latin prefix 're-' meaning 'again' combined with the derivative 'activator' (from 'activate'), where 'activate' comes from Latin elements related to 'act-' meaning 'to do or drive'.

're-activator' was formed in modern English by prefixing 're-' to 'activator' (which itself derives from 'activate'); 'activate' descends from Late Latin/Latin roots related to 'activus' and the verb-forming element from Latin 'agere'/'act-'.

Initially the components referred simply to 'doing' or 'making active'; over time the compound came to mean specifically 'one that makes active again' (i.e., restores previous activity).