'unenthusiastically' originates from the prefix 'un-' meaning 'not' and the word 'enthusiastic,' which comes from the Greek word 'enthousiasmos,' meaning 'inspiration or possession by a god.'

'enthousiasmos' transformed into the Latin word 'enthusiasmus,' and eventually became the modern English word 'enthusiastic,' with 'un-' added to form 'unenthusiastic.'

Initially, 'enthousiasmos' meant 'inspiration or possession by a god,' but over time it evolved into its current meaning of 'having or showing intense and eager enjoyment, interest, or approval.'