Bound to be busy (4,2)
I believe the answer is:
tied up
I believe this is a double definition.
'bound' is the first definition.
('tie up' can be a synonym of 'bind')
'be busy' is the second definition.
('tied up' can be similar in meaning to 'busy')
'to' is the link.
(Other definitions for tied up that I've seen before include "busy" , "Thus prisoner may be kept" , "Secured; engaged" .)