Off - or working (5)
I believe the answer is:
going
I believe this is a double definition.
'off' is the first definition.
(both can mean departing)
'working' is the second definition.
(working can mean going or activated)
'or' acts as a link.
(Other definitions for going that I've seen before include "Ground condition for horse racing" , "on the way out" , "Disappearing" , "in action" , "State of ground (racing)" .)