'proportional' originates from Latin, specifically the word 'proportionalis', where 'pro-' meant 'for' and 'portio' meant 'part or share'.

'proportionalis' transformed into the Old French word 'proportionel', and eventually became the modern English word 'proportional'.

Initially, it meant 'having a relation in degree or number', and this meaning has largely remained the same in modern usage.