'synergism' originates from Greek via New/Modern Latin, specifically the Greek word 'synergia' (συνεργία), where 'syn-' meant 'together' and 'ergon' meant 'work'.

'synergia' passed into Late Latin/New Latin forms (e.g. 'synergismus'/'synergia') and was adopted into English in the 18th–19th century as 'synergism' (with the -ism suffix).

Initially it meant 'working together' or 'joint action', and over time it evolved into the modern sense of 'cooperative interaction producing a greater combined effect'.