'unimprovable' originates from the prefix 'un-' meaning 'not' and the word 'improvable' which comes from 'improve', derived from the Latin 'improbare', where 'in-' meant 'in' and 'probare' meant 'to test or prove'.

'improbare' transformed into the Old French word 'emprover', and eventually became the modern English word 'improve', leading to the formation of 'unimprovable'.

Initially, 'improve' meant 'to make better', and 'unimprovable' has retained the meaning of 'not capable of being made better'.