'immeasurability' originates from Latin via Old French and Middle English, specifically from the negative prefix 'in-' (from Latin 'in-' meaning 'not'), the root 'measure' (from Old French 'mesure', from Latin 'mensura' meaning 'a measuring'), and the noun-forming suffix '-ity'.

'measure' came into English from Old French 'mesure' (from Latin 'mensura'), 'immeasurable' was formed in Middle English by prefixing 'in-' to 'measurable', and the modern noun 'immeasurability' was produced by adding the suffix '-ity' to form the abstract noun.

Initially it meant 'not capable of being measured' in a literal sense; over time it also acquired figurative senses of 'extreme' or 'boundless' that emphasize vastness or immeasurable impact.