Move or be going to move (6)
I believe the answer is:
bestir
'move' is the definition.
(bestirring is a kind of moving)
'be going to move' is the wordplay.
'going to' means one lot of letters go next to another.
'move' becomes 'stir' (stir can mean to make a movement).
'be'+'stir'='BESTIR'
'or' acts as a link.
(Other definitions for bestir that I've seen before include "move" , "Rouse (oneself)" , "Become active" , "Exert/rouse (oneself)" .)