Organ observed outside playing Liszt preludes (6)

I believe the answer is:

spleen

I'm a little stuck... Click here to teach me more about this clue!

'organ' is the definition.
(the spleen is an organ)

I don't understand how the remainder of the clue works.

(Other definitions for spleen that I've seen before include "Organ supposedly controlling temper" , "Soft organ near the stomach" , "Abdominal organ - bad temper" , "Body organ or bad temper" , "Organ of the body - ill temper" .)

I've seen this clue in The Guardian.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.