A copper gives soldiers insight (6)
I believe the answer is:
acumen
'insight' is the definition.
(I've seen this in another clue)
'a copper gives soldiers' is the wordplay.
I cannot really see how this works, but
'a' is present in the answer.
'copper' could be 'cu' (chemical symbol) and 'cu' is located in the answer.
'soldiers' could be 'men' (men can mean a group of soldiers) and 'men' is present in the answer.
No letters remain.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for acumen that I've seen before include "'Shrewdness, astuteness (6)'" , "Sagicity as in business" , "brightness" , "Shrewdness, sharpness of mind" , "ability to make good judgements" .)