Military unit doesn't finish diet (7)
I believe the answer is:
regimen
'diet' is the definition.
(a diet is a certain eating regimen)
'military unit doesn't finish' is the wordplay.
'military unit' becomes 'regiment' (regiment is a kind of military unit).
'doesn't finish' 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 "Systematic course of treatment, diet, etc" , "Plan for e.g. diet" , "Recommended course" , "recommended diet" , "Therapeutic programme (of diet and exercise)" .)