'proportionately' originates from Latin, specifically the word 'proportio,' where 'pro-' meant 'for' and 'portio' meant 'part or share.' 'Related' comes from Latin 'relatus,' the past participle of 'referre,' meaning 'to bring back.'

'Proportio' transformed into the Old French word 'proportion,' and eventually became the modern English word 'proportion.' 'Relatus' transformed into the Old French word 'relater,' and eventually became the modern English word 'relate.'

Initially, 'proportionately' meant 'in a manner that is proportionate,' and this meaning has largely remained the same in modern usage.