Organ used in Baroque arias (3)
I believe the answer is:
ear
'organ' is the definition.
(ear is a kind of organ)
'in baroque arias' is the wordplay.
'in' indicates a hidden word.
'EAR' is hidden in the letters of 'baroque arias'.
'used' is the link.
(Other definitions for ear that I've seen before include "Part of cereal plant containing seed" , "one hears" , "Corn seed-holder" , "Shell-like (slang)" , "'Give every man thine ..., but few thy voice' (Hamlet)" .)