Soldiers circle large fungus (7)
I believe the answer is:
parasol
'fungus' is the definition.
(parasol is a type of mushroom)
'soldiers circle large' is the wordplay.
'soldiers' becomes 'paras' (para is a kind of soldier).
'circle' becomes 'O' (O is a circle).
'large' becomes 'L' (eg in clothes sizes).
'paras'+'o'+'l'='PARASOL'
(Other definitions for parasol that I've seen before include "Sunshade" , "Protection from sun" , ""Sunbrella"" , "Protection from light" , "aeroplane" .)