Ardour (7)
(Other definitions for passion that I've seen before include "Rage" , "Intense emotion, anger or love" , "Fervent love" , "Ardent emotion" , "fire" .)
'ardour' is the definition.
(synonyms)
This is the entire clue.
(Other definitions for fervour that I've seen before include "Passionate feeling" , "Passion" , "Enthusiasm - excitement" , "Heated feeling" , "Feelings of great warmth and intensity" .)