'unflappable' originates from English, specifically the word 'flap,' where 'un-' is a prefix meaning 'not,' and 'flap' meant 'to become agitated or excited.'

'flap' changed from the Old English word 'flæppan' and eventually became the modern English word 'flap,' with 'unflappable' emerging as a negation of the state of being flappable.

Initially, 'flap' meant 'to move or sway with a noise,' but over time it evolved into its current meaning of 'to become agitated or excited,' with 'unflappable' meaning the opposite.