'rationale' originates from Latin, specifically the word 'rationalis,' where 'ratio' meant 'reason' and '-alis' was a suffix forming adjectives.

'rationalis' transformed into the French word 'rationnel,' and eventually became the modern English word 'rationale' through Middle English.

Initially, it meant 'pertaining to reason,' but over time it evolved into its current meaning of 'a set of reasons or logical basis.'