Speed of journey? (10)
I believe the answer is:
expedition
I believe this is a double definition.
'speed' is the first definition.
(expedition is a kind of speed)
'journey?' is the second definition.
(expedition is a kind of journey)
'of' is the link.
(Other definitions for expedition that I've seen before include "Promptness" , "Speed is the essence" , "Dispatch" , "journey" , "Voyagers" .)