'addlebrained' originates from Middle English, specifically the word 'adel,' where 'adel' meant 'liquid filth or urine.'

'adel' transformed into the English word 'addle,' which initially meant 'to make or become rotten,' and eventually became the modern English word 'addlebrained' to describe a confused state of mind.

Initially, it meant 'rotten or putrid,' but over time it evolved into its current meaning of 'confused or muddled in thought.'