Heed military order (9)
I believe the answer is:
attention
This clue is a double definition.
'heed' is the first definition.
(I've seen this before)
'military order' is the second definition.
('attention' can be given as a military order)
(Other definitions for attention that I've seen before include "Special care, soldier's position" , "Applicaton, concentration" , "Vigilance; care" , "Keen students pay this" , "careful thought" .)