Amusing US soldier providing mushrooms (5)
I believe the answer is:
fungi
'mushrooms' is the definition.
(I've seen this before)
'amusing us soldier' is the wordplay.
'amusing' becomes 'fun' (synonyms).
'us soldier' becomes 'GI' (GI can mean an American soldier).
'fun'+'gi'='FUNGI'
'providing' acts as a link.
(Other definitions for fungi that I've seen before include "life in woodland?" , "woodland feature" , "Eg, toadstools" , "Plants like mushrooms and toadstools" , "Group with some killers" .)