'activatory' originates from Latin, specifically from the verb 'activare' and the adjective 'activus', where the root 'activ-' meant 'active'. The English adjective is formed with the suffix '-ory' (from Latin '-orius') meaning 'pertaining to' or 'having the function of'.

'activatory' developed via the Latin formation (activare/activus → activatorius) and through Neo‑Latin/late formation patterns into English as 'activatory' (from 'activate' + '-ory').

Initially it meant 'pertaining to or causing activation' and over time has retained that sense of 'producing or promoting activity' in technical and scientific contexts.