Occupied (2 wds.) (6)
'occupied' is the definition.
(similar in meaning)
This is all the clue.
(Other definitions for busy that I've seen before include "detective" , "Active (as a bee?)" , "Full of activity" , "Without leisure" , "With lots to do" .)
(Other definitions for tiedup that I've seen before include "Is busy" , "wrapped a present" .)