Army unit's diet close to front (8)
I believe the answer is:
regiment
'army unit's' is the definition.
(regiment is a kind of army unit)
'diet close to front' is the wordplay.
'diet' becomes 'regime'.
'close' becomes 'n' (I can't explain this - if you can you should give a lot more credence to this answer).
'front' says to take the initial letters.
The initial letter of 'to' is 't'.
'regime'+'n'+'t'='REGIMENT'
Can you help me to learn more?
(Other definitions for regiment that I've seen before include "Military group" , "Organise; army unit" , "Brigade" , "Force under colonel" , "The Grenadier Guards, for example" .)