'airbrained' originates from the combination of 'air' and 'brained', where 'air' suggests emptiness or lack of substance, and 'brained' refers to the mind or intelligence.

'airbrained' evolved from the concept of having one's head filled with air, implying a lack of serious thought or intelligence.

Initially, it meant 'having one's head filled with air', but over time it evolved into its current meaning of 'lacking intelligence or common sense'.