15 across
Soldiers
wait
on
order
(7)
Soldiers wait on order (7)
hints
0
checks
0
hints
The definition is at the end of the clue.
How the clue works
The definition is order, as in to reserve or book something. We build it from RE for the Royal Engineers (our 'soldiers') followed by SERVE meaning 'wait on', running them together to give RESERVE.