Wink - can't tie knot (7)
I believe the answer is:
nictate
'wink' is the definition.
(I know that wink can be written as nictate)
'can't tie knot' is the wordplay.
'knot' is an anagram indicator (I've seen 'knotted' mean this).
'cant'+'tie'='canttie'
'canttie' with letters rearranged gives 'NICTATE'.
(Other definitions for nictate that I've seen before include "Blink - enact it (anag)" , "Wink" , "shut their eyes momentarily" .)