Jacket father fastened round chest (5)
I believe the answer is:
parka
'jacket father' is the definition.
'parka' can be an answer for 'jacket' (I've seen this before). I am unsure of the 'father' bit.
'fastened round chest' is the wordplay.
'fastened' becomes 'pa' (I can't justify this - if you can you should believe this answer much more).
'round' means one lot of letters goes inside another.
'chest' becomes 'ark' (historical term for a chest).
'pa' going around 'ark' is 'PARKA'.
Can you help me to learn more?
(Other definitions for parka that I've seen before include "Short, hooded coat" , "cover plus hood attachment" , "Hooded warm jacket" , "hoodie" , "Windproof jacket" .)