Amuse nuts turned on in music bar (7)
I believe the answer is:
measure
'music bar' is the definition.
(measure can mean a bar of music)
'amuse nuts turned on' is the wordplay.
I cannot really see how this works, but
an anagram of 'amuse' is 'measu' which is located in the answer.
'on' could be 're' ('on' can be mean 'with reference to') and 're' is found in the answer.
This accounts for all the letters.
This may be the basis of the clue (or it may be nonsense).
'in' acts as a link.
Can you help me to learn more?
(Other definitions for measure that I've seen before include "The size of a dance" , "Determine the size of" , "Action - amount" , "Magnitude" , "Find the size" .)