Bop on the head
I believe the answer is:
conk
'bop on the head' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for conk that I've seen before include "Nose (colloq.)" , "Hooter" , "Slangy nose or head" , "(Slang) nose - head" , "Nose; break down" .)