Conk on the head (3)
I believe the answer is:
bop
'conk on the head' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for bop that I've seen before include "Dance - hit (informal)" , "Form of jazz from the 1940s" , "Dance to record" , "Lively dance" , "Dance of the 1950s" .)