Tie finally put on to twist and knot (4)
I believe the answer is:
node
'knot' is the definition.
(both can mean a swollen lump)
'tie finally put on to twist' is the wordplay.
'finally' says to take the final letters.
'put on' becomes 'don' (as in donning or putting on an item of clothing).
'to twist' says the letters should be written in reverse (I've seen 'twisting' mean this (letters twist back)).
The final letter of 'tie' is 'e'.
'e'+'don'='edon'
'edon' written backwards gives 'NODE'.
'and' acts as a link.
(Other definitions for node that I've seen before include "Thickened enlargement" , "growth" , "Done to a small lump" , "Point of intersection" , "Intersection in a network" .)