Hearing about organ (3)
I believe the answer is:
ear
'organ' is the definition.
(ear is a kind of organ)
'hearing about' is the wordplay.
'about' indicates a hidden word.
'EAR' is hidden within 'hearing'.
(Other definitions for ear that I've seen before include "Shell-like; corn" , "Lend one and listen" , "cut" , "Seed-bearing part of corn" , "Aural organ" .)