Rush as tempo maintains speed (5)
I believe the answer is:
haste
'speed' is the definition.
(I know that haste is a type of speed)
'rush as tempo maintains' is the wordplay.
'maintains' says the answer is hidden in the clue (I've seen 'maintaining' mean this (the solution is held or maintained within the clue)).
'HASTE' can be found hidden inside 'rush as tempo'.
(Other definitions for haste that I've seen before include "Expeditiousness" , "Over-eager speed" , "dispatch" , "''Marry in . . . . ., repent at leisure''" , "velocity" .)