Register for work (4)
I believe the answer is:
till
This clue is a double definition.
'register' is the first definition.
(thesaurus)
'work' is the second definition.
(tilling is a kind of working)
'for' is the link.
(Other definitions for till that I've seen before include "Work on farm" , "Cashbox" , "Drawer holding money in shop." , "Small box in shop for holding cash" , "Up to (a point in time)" .)