'balloonful' originates from English, specifically formed from the noun 'balloon' plus the suffix '-ful', where the suffix '-ful' meant 'full of'.

'balloon' entered English from French 'ballon', which in turn came from Italian 'ballone' (an augmentative of 'palla' meaning 'ball'); the English compound 'balloonful' was later formed by adding the productive suffix '-ful' to 'balloon'.

Initially it referred straightforwardly to the quantity that fills a balloon; over time the meaning has remained essentially the same as 'an amount that fills a balloon'.