This is the 4982nd most frequent Swedish word.
brunna
To burn.
Here, 'brunna' is used in its literal sense of something catching fire and burning.
Skogen började brunna vid middagstid.
The forest started burning at noon.
In this phrase, 'brunna' metaphorically describes diminishing intensity or enthusiasm, with 'ut' indicating the completion of the action.
Passionen för musik verkar aldrig brunna ut.
The passion for music seems never to burn out.
Here, 'brunna' is used metaphorically to express a strong emotional state, like inner fire or excitement.