Garment, one carried by old king on way back (5)
I believe the answer is:
tunic
'garment' is the definition.
(tunic is a kind of garment)
'one carried by old king on way back' is the wordplay.
'one' becomes 'i' (Roman numeral).
'carried by' is an insertion indicator.
'old king' becomes 'cnut' (King Cnut).
'on way back' says the letters should be written backwards.
'i' going within 'cnut' is 'cinut'.
'cinut' reversed gives 'TUNIC'.
(Other definitions for tunic that I've seen before include "piece of clothing" , "Roman garment" , "Jacket of some soldiers" , "Smock" , "Close fitting jacket as part of uniform" .)