Girl entertaining leader of Russian troops (4)
I believe the answer is:
army
'troops' is the definition.
(I've seen this in another clue)
'girl entertaining leader of russian' is the wordplay.
'girl' becomes 'amy' ().
'entertaining' is an insertion indicator.
'leader of' suggests taking the first letters.
The initial letter of 'russian' is 'r'.
'amy' going around 'r' is 'ARMY'.
(Other definitions for army that I've seen before include "Land-fighting force" , "Throng" , "Body of people organised for war" , "Vast number" , "Large host" .)