'proportionally' originates from Latin, specifically the word 'proportio', where 'pro-' meant 'for' or 'forward' and 'portio' meant 'a part or share'.

'proportionally' developed from the adjective 'proportional', which comes from Middle English 'proportion' (from Old French 'proportion'), itself from Latin 'proportio'. The adverbial suffix '-ally' (from Latin '-alis') was later added to form 'proportionally'.

Initially related to the idea of a 'part' or 'share' ('proportio'), it came to mean the relation of parts to each other and later 'in a corresponding degree' as the adverb 'proportionally'.