Professional wearing article of protective clothing (5)
I believe the answer is:
apron
'protective clothing' is the definition.
(I've seen this before)
'professional wearing article' is the wordplay.
'professional' becomes 'pro' (abbreviation).
'wearing' indicates putting letters inside.
'article' becomes 'an' (indefinite article).
'pro' going into 'an' is 'APRON'.
'of' acts as a link.
(Other definitions for apron that I've seen before include "Kitchen garment or airfield area" , "Domestic protection" , "conveyor-belt" , "Airport area for manoeuvring and loading planes" , "Area for aircraft not in use" .)