Great US soldier in raincoat (5)
I believe the answer is:
magic
'great' is the definition.
(both can mean very good)
'us soldier in raincoat' is the wordplay.
'us soldier' becomes 'GI' (informal term for a US soldier).
'in' indicates putting letters inside.
'raincoat' becomes 'mac' (macintosh is a type of raincoat).
'gi' going within 'mac' is 'MAGIC'.
(Other definitions for magic that I've seen before include "Superb" , "Great" , "Prestidigitation" , "Brilliant -- deception" , "Tricks" .)