A copper gives soldiers intelligence (6)
I believe the answer is:
acumen
'intelligence' is the definition.
(I know that acumen is a type of astuteness)
'a copper gives soldiers' is the wordplay.
I cannot really see how this works, but
'a' is found in the answer.
'copper' could be 'cu' (Cu is the chemical symbol for copper) and 'cu' is found within the answer.
'soldiers' could be 'men' (men can mean a group of soldiers) and 'men' is located 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 "Forming judgement" , "Sharpness, penetration, quickness of perception" , "Insightfulness" , "The ability to make good and quick decisions" , "brightness" .)