'reductionistic' originates from English, specifically formed from the noun 'reduction' plus the adjectival suffix '-istic', where 'reduction' ultimately comes from Latin 'reducere' (re- 'back' + ducere 'to lead').

'reduction' came into English via Latin 'reductio'/'reducere' (and Old French influence) and entered Middle English as 'reduction'; the modern adjective 'reductionistic' was formed in modern English by adding '-istic' (from French/Latin '-isticus', from Greek '-istikos').

Initially, the Latin root meant 'to lead back' or 'bring back'; over time 'reduce' and 'reduction' took on senses of 'bring to a smaller size or simpler form', and 'reductionistic' evolved to mean 'characterized by explaining things by reducing them to simpler parts' (sometimes with a critical sense of oversimplification).