Loud organ causing fright (4)
I believe the answer is:
fear
'fright' is the definition.
(synonyms)
'loud organ' is the wordplay.
'loud' becomes 'f' (short for forte - 'loud' in music).
'organ' becomes 'ear' (the ear is an organ).
'f'+'ear'='FEAR'
'causing' acts as a link.
(Other definitions for fear that I've seen before include "Cutting edge" , "Apprehension" , "awe" , "Qualms" , "Consternation" .)