'apportionability' originates from English, specifically from the verb 'apportion' combined with the noun-forming suffix '-ability' (from Latin-derived '-abilitas'), where 'apportion' ultimately relates to Latin 'portio' meaning 'a part' or 'portion'.

'apportion' changed from Old French/Anglo-French forms such as 'aporcioner' and Middle English 'apportionen' and eventually became modern English 'apportion'; the suffix '-ability' developed via Old French/Latin '-abilitas' to form nouns indicating capability, producing 'apportionability' in modern English.

Initially related to the idea of a 'portion' or 'share' (from Latin 'portio'), over time the derived forms came to express the capability or suitability of being given as a portion; thus 'apportionability' means the capability of being apportioned.