Knot; obligation (3)
I believe the answer is:
tie
I believe this clue is a double definition.
'knot' is the first definition.
(I know that knot is a more specific form of the action bind)
'obligation' is the second definition.
(I've seen this before)
(Other definitions for tie that I've seen before include "Equality of score" , "A draw or male neckwear" , "Stalemate" , "line above notes" , "Draw; link" .)