Loud expert features (4)
I believe the answer is:
face
'features' is the definition.
(thesaurus)
'loud expert' is the wordplay.
'loud' becomes 'f' (A musical term**).
'expert' becomes 'ace' (ace is a kind of expert).
'f'+'ace'='FACE'
(Other definitions for face that I've seen before include "set of features" , "Outward appearance" , "Confront - mug (slang)" , "'Cheeks, mouth, eyes etc (4)'" , "cheek" .)