1 : characterized by warmth of feeling typically expressed in eager zealous support or activity
2 : fiery, hot
3 : shining, glowing
1 : an ardent admirer ardent fans
2 : an ardent sun
3 : ardent eyes –merriam-webster
I only knew the first definition for this word, although 2 and 3 make a lot of sense for GMs and players to use. You could describe the heat off the dragon’s breath weapon, or the holy aura of a herald with these.