I've a radio — listener engaged there (3)
I believe the answer is:
ear
'i've a radio listener engaged there' is the definition.
I can't tell whether this defines the answer.
'i've a radio listener engaged there' is the wordplay.
'engaged there' indicates the answer is hidden within the clue.
'EAR' can be found hidden inside 'ive a radio listener'.
(Other definitions for ear that I've seen before include "Organ of hearing" , "Listener in the cornfield" , "Seed-bearing part of corn" , "Part of corn plant" , "Shell-like (slang)" .)