Secure measure of speed for flyer (4)
I believe the answer is:
knot
I believe this clue is a quadruple definition!!
'secure' is the first definition.
(I know that knot is a type of bind)
'measure' is the second definition.
(knot is a kind of measure)
'of' acts as a link.
'speed' is the third definition.
(I've seen this before)
'for flyer' is the fourth definition.
(type of bird)
(Other definitions for knot that I've seen before include "Fastener - bird - unit of speed at sea" , "To secure < > bird" , "Bird; tie securely" , "Unit of length used in navigation" , "Nodule" .)