Shrewd enough to keep a cool head at the bar (6)
I believe the answer is:
clever
'shrewd' is the definition.
(I've seen this in another clue)
'enough to keep a cool head at the bar' is the wordplay.
I cannot really understand how this works, but
'bar' could be 'lever' (lever is a kind of bar) and 'lever' is present in the answer.
A single letter 'c' remains which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for clever that I've seen before include "Adroit, ingenious" , "Gifted" , "Good or quick at learning" , "Smart or shrewd" , "Quick at learning, talented" .)