Split, as with an axe (6)
I believe the answer is:
cleave
'split as with an axe' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for cleave that I've seen before include "Split apart - stick together" , "Split or cling to" , "Fissure" , "To separate and to adhere" , "Cut (with an axe?)" .)