Great enthusiasm or passion (6)
I believe the answer is:
ardour
I believe this clue is a double definition.
'great enthusiasm' is the first definition.
(I've seen this before)
'passion' is the second definition.
(I know that ardour is a type of passion)
(Other definitions for ardour that I've seen before include "Great fire" , "Fervour, zeal" , "Intense feeling (of love?)" , "Fervency" , "Fervour or passion" .)