Weatherproof coat old man wrapped round chest (5)
I believe the answer is:
parka
'weatherproof coat' is the definition.
'old man wrapped round chest' is the wordplay.
'old man' becomes 'pa' (both can mean father).
'wrapped round' is an insertion indicator.
'chest' becomes 'ark' (historical term for a chest).
'pa' going around 'ark' is 'PARKA'.
(Other definitions for parka that I've seen before include "Warm, hooded coat" , "Short, hooded coat" , "Weatherproof jacket with hood" , "cover plus hood attachment" , "Anorak" .)