'barmybrained' originates from English, specifically the words 'barmy' and 'brain', where 'barmy' (from dialect 'barm') originally meant 'frothy' and later 'foolish', and 'brain' (from Old English 'brægen') meant 'brain'.

'barmy' changed from the dialect word 'barm' meaning 'yeast foam' and came to be used figuratively as 'foolish'; 'brain' comes from Old English 'brægen'; the compound 'barmy-brained' developed in colloquial English to describe someone with a foolish mind and eventually formed the single word 'barmybrained'.

Initially, 'barmy' referred to 'frothy' or relating to 'barm', but over time it evolved to mean 'foolish' or 'mad', and the compound's meaning became 'having a foolish or unsound mind'.