'nonadjustable' originates from Modern English, specifically formed from the negative prefix 'non' (originally Latin 'non') and the adjective 'adjustable' (from Old French 'ajuster'/'ajuster' via Middle English), where 'non' meant 'not' and 'adjustable' meant 'able to be adjusted'.

'adjustable' changed from Old French 'ajuster' (meaning 'to fit, make right') through Middle English into 'adjust', then took the suffix '-able' (from Latin/French) to make 'adjustable'; the negative prefix 'non-' was later added in Modern English to form 'nonadjustable'.

Initially the elements meant 'not' + 'able to be adjusted', and over time this compound has kept the straightforward meaning 'not able to be adjusted'.