A pro wearing long apron (8)
I believe the answer is:
pinafore
'apron' is the definition.
(I've seen this before)
'a pro wearing long' is the wordplay.
'pro' becomes 'for' (I've seen this before).
'wearing' is an insertion indicator.
'long' becomes 'pine' (to pine for someone is to long for them).
'a'+'for'='afor'
'afor' put inside 'pine' is 'PINAFORE'.
(Other definitions for pinafore that I've seen before include "Musical craft" , "Sleeveless apron-like dress" , "HMS -- (G&S)" , "gives homely protection" , "Gilbert & Sullivan operetta 'HMS ........'" .)