They order the troops salad (3)
I believe the answer is:
cos
This clue is a double definition.
'they order the troops' is the first definition.
(COs is short for commanding officers)
'salad' is the second definition.
(I've seen this before)
(Other definitions for cos that I've seen before include "A long-leaved lettuce" , "often associated with sin" , "Variety of lettuce" , "providing unsatisfactory explanation?" , "leaves > function" .)