Stick or split? (6)
I believe the answer is:
cleave
This clue is a double definition.
'stick' is the first definition.
(I've seen this before)
'split?' is the second definition.
('cleave' can be a synonym of 'split')
'or' acts as a link.
(Other definitions for cleave that I've seen before include "Join or split" , "remain attached" , "Split apart - stick together" , "Split or cling to" , "Split with the grain" .)