Pretty loud song (4)
I believe the answer is:
fair
'pretty' is the definition.
(thesaurus)
'loud song' is the wordplay.
'loud' becomes 'f' (A musical term).
'song' becomes 'air' (I've seen this before**).
'f'+'air'='FAIR'
(Other definitions for fair that I've seen before include "Just treatment of others" , "honest" , "Blonde; impartial" , "light headed" , "Even-handed travelling show?" .)