'appassionate' originates from Italian, specifically the verb 'appassionare' and the adjective 'appassionato', where the root 'passione' meant 'passion'.

'appassionate' entered English as a borrowing from Italian musical/expressive terminology (compare Italian 'appassionato' used as a performance direction) and was adapted into English as 'appassionate.'

Initially used in musical contexts to indicate playing 'with passion' or 'with great feeling'; over time it has been used more broadly to mean 'filled with or producing strong emotion,' a core meaning that has been largely preserved.