Redhead not quite breaking stick (6)
I believe the answer is:
adhere
'stick' is the definition.
(to adhere to something is to stick to it)
'redhead not quite breaking' is the wordplay.
'not quite' means to remove the last letter (most but not all of the word).
'breaking' is an anagram indicator.
'redhead' with its final letter taken away is 'redhea'.
'redhea' with letters rearranged gives 'ADHERE'.
(Other definitions for adhere that I've seen before include "Stick to or remain faithful" , "Stick - join" , "Stick to or continue faithful" , "Hold fast, stand by" , "Stick L" .)