Conjuring soldier in coat (5)
I believe the answer is:
magic
'conjuring' is the definition.
(I've seen this before)
'soldier in coat' is the wordplay.
'soldier' becomes 'GI' (GI can mean a US soldier).
'in' means one lot of letters goes inside another.
'coat' becomes 'mac' (mac is a kind of coat).
'gi' placed inside 'mac' is 'MAGIC'.
(Other definitions for magic that I've seen before include "'Charms, spells, illusions (5)'" , "Conjuror's art" , "Illusory feat" , "Spelling?" , "Art that supposedly invokes supernatural powers" .)