It may get tied at speed (4)
I believe the answer is:
knot
'speed' is the definition.
(knot is a nautical measure of speed)
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for knot that I've seen before include "Interlacement" , "Bend - one nautical mile per hour" , "Tight interlacing of cord, string etc" , "binder?" , "Unit of speed used by ships" .)