Acknowledge head of music in entrance (5)
I believe the answer is:
admit
'acknowledge' is the definition.
('admit' can be a synonym of 'acknowledge')
'head of music in entrance' is the wordplay.
'head of' indicates taking the first letters.
'in' indicates putting letters inside.
'entrance' becomes 'adit' (I've seen this before).
The first letter of 'music' is 'm'.
'm' going within 'adit' is 'ADMIT'.
(Other definitions for admit that I've seen before include "Let in - concede" , "Confess; allow in" , "Allow entry" , "Provide student with place" , "Allow to enter; own up" .)