Busy person with loud complaint (4)
I believe the answer is:
beef
'complaint' is the definition.
(thesaurus)
'busy person with loud' is the wordplay.
'busy person' becomes 'bee' (I've seen this in other clues**).
'with' means one lot of letters go next to another.
'loud' becomes 'f' (A musical term).
'bee'+'f'='BEEF'
(Other definitions for beef that I've seen before include "Bovine flesh" , "Complaint; strength" , "Brawn; complaint" , "Meat of the cow" , "Type of meat" .)