Military unit not finishing diet (7)
I believe the answer is:
regimen
'diet' is the definition.
(a diet is a certain eating regimen)
'military unit not finishing' is the wordplay.
'military unit' becomes 'regiment' (regiment is a kind of military unit).
'not finishing' means to remove the last letter.
'regiment' with its final letter taken off is 'REGIMEN'.
(Other definitions for regimen that I've seen before include "(In medicine) a systematic plan for therapy" , "discipline" , "recommended diet" , "Systematic course of treatment, diet, etc" , "Recommended course" .)