'photosynthetic' originates from Greek, specifically the word 'photosynthesis,' where 'photo-' meant 'light' and 'synthesis' meant 'putting together.'

'photosynthesis' transformed into the adjective 'photosynthetic' to describe processes or organisms involved in photosynthesis.

Initially, it meant 'related to the process of photosynthesis,' and this meaning has largely remained the same in modern usage.