'proportionately-assigned' is a modern English compound combining 'proportionately' and 'assigned'. 'proportionately' ultimately originates from Latin 'proportio' ('pro-' meaning 'toward' + 'portio' meaning 'share'), developing via Old French and Middle English into 'proportion'/'proportionate' + the adverbial suffix '-ly'. 'assigned' derives from Latin 'assignare' ('ad-' meaning 'to' + 'signare' meaning 'mark, sign'), via Old French 'assigner' and Middle English 'assignen'.

'proportio' developed into Old French 'proporcion' and Middle English 'proporcioun', yielding 'proportion' and later 'proportionate' > 'proportionately'. Latin 'assignare' became Old French 'assigner', then Middle English 'assignen' > Modern English 'assign'/'assigned'. The hyphenated compound 'proportionately-assigned' reflects modern English compounding conventions.

The components retained their core senses ('in proportion' and 'allocated/appointed'). As a compound adjective, the phrase came to mean 'allocated according to proportion' in contemporary usage.