Nervous of loud rebuke (7)
I believe the answer is:
fearful
'nervous' is the definition.
(thesaurus)
'loud rebuke' is the wordplay.
'loud' becomes 'f' (short for forte - 'loud' in music).
'rebuke' becomes 'earful' (earful is a kind of rebuke).
'f'+'earful'='FEARFUL'
'of' acts as a link.
(Other definitions for fearful that I've seen before include "Timid" , "Timorous; terrible" , "Afraid; very great" , "awful!" , "Scared" .)