'treatment-related' originates from the combination of 'treatment' and the suffix '-related', where 'treatment' refers to medical care and '-related' indicates a connection or association.

The term 'treatment' comes from the Old French 'traitement', which means 'management' or 'handling', and '-related' is a modern English suffix used to denote association.

Initially, 'treatment' referred to the act of managing or handling, but over time it evolved to specifically mean medical care or therapy.