'assuefaction' originates from Old French, specifically the word 'assouefacion', where the Latin root 'assuescere' (from ad- + suescere) meant 'to become accustomed'.

'assuefaction' changed from the Old French word 'assouefacion' (and is ultimately related to Latin 'assuescere' / 'assuefacere') and eventually became the modern English word 'assuefaction' through Middle English usage.

Initially, it meant 'the process of becoming accustomed', but over time it evolved into its current meaning of 'habitual conditioning or accustoming' (and in some older texts could imply 'addiction' or strong habit).