Energy, speed (3)
I believe the answer is:
zip
I believe this clue is a double definition.
'energy' is the first definition.
(I know that energy can be written as zip)
'speed' is the second definition.
(I know that speed can be written as zip)
(Other definitions for zip that I've seen before include "closer" , "Nothing < close up" , "Locking device with two toothed edges and a sliding tab" , "drive" , "Type of fastener" .)