A hitch, perhaps, at speed (4)
I believe the answer is:
knot
I believe this is a double definition.
'a hitch perhaps' is the first definition.
(I know that hitch is a type of knot)
'speed' is the second definition.
(knot is a nautical measure of speed)
'at' is the link.
(Other definitions for knot that I've seen before include "one may find in wood" , "Air mile" , "Tangled mass" , "Tie, hitch" , "securing tie" .)