Mutilated head on stick (6)
I believe the answer is:
adhere
'stick' is the definition.
(to adhere to something is to stick to it)
'mutilated head on' is the wordplay.
'mutilated' indicates anagramming the letters.
'on' becomes 're' (regarding).
'head' anagrammed gives 'adhe'.
'adhe'+'re'='ADHERE'
(Other definitions for adhere that I've seen before include "Keep" , "Remain attached" , "Stick - join" , "Stick to or continue faithful" , "Hold fast, stand by" .)