Scared of a loud attack (6)
I believe the answer is:
afraid
'scared' is the definition.
(similar in meaning)
'a loud attack' is the wordplay.
'loud' becomes 'f' (short for forte - 'loud' in music).
'attack' becomes 'raid' (raiding is a kind of attacking).
'a'+'f'+'raid'='AFRAID'
'of' is the link.
(Other definitions for afraid that I've seen before include "Feeling anxiety or fear" , "Scared, apprehensive" , "Fearful, anxious" , "Scared - politely regretful" , "Fearful and timid" .)