Organ starts to echo around room (3)
I believe the answer is:
ear
'organ' is the definition.
(the ear is an organ)
'starts to echo around room' is the wordplay.
'starts to' says to take the initial letters.
The initial letters of 'echo around room' is 'EAR'.
(Other definitions for ear that I've seen before include "'Give every man thine ..., but few thy voice' (Hamlet)" , "Fruiting head of corn" , "Head of, eg, corn" , "Heed" , "Discernment musicians need" .)