Military group doesn’t finish diet (7)
I believe the answer is:
regimen
'diet' is the definition.
(a diet is a certain eating regimen)
'military group doesn't finish' is the wordplay.
'military group' becomes 'regiment' (group of soldiers).
'doesn't finish' means to remove the last letter.
'regiment' with its final letter removed is 'REGIMEN'.
(Other definitions for regimen that I've seen before include "Government - course of treatment" , "prescribed treatment" , "Prescribed way of life like diet" , "discipline" , "Therapeutic programme (of diet and exercise)" .)