In favour of wearing an item of protective clothing (5)
I believe the answer is:
apron
'item of protective clothing' is the definition.
(I've seen this before)
'in favour of wearing an' is the wordplay.
'in favour of' becomes 'pro' (I've seen this before).
'wearing' means one lot of letters goes inside another.
'pro' going into 'an' is 'APRON'.
(Other definitions for apron that I've seen before include "Protective garment worn at front" , "Paved surface where aircraft stand when not in use" , "that's used by Oliver!?" , "area in front of aircraft hangar" , "Protective garment - part of stage" .)