Professional wears a new pinafore (5)
I believe the answer is:
apron
'pinafore' is the definition.
(I've seen this in another clue)
'professional wears a new' is the wordplay.
'professional' becomes 'pro' (synonyms).
'wears' indicates putting letters inside.
'new' becomes 'n' (common abbreviation eg NT for New Testament).
'a'+'n'='an'
'pro' put within 'an' is 'APRON'.
(Other definitions for apron that I've seen before include "Area for aircraft not in use" , "Paved surface where aircraft stand when not in use" , "item of protective clothing" , "Protective cover" , "Protective garment in kitchen" .)