Vim, vigour (6)
I believe the answer is:
energy
I believe this clue is a double definition.
'vim' is the first definition.
(synonyms)
'vigour' is the second definition.
(synonyms)
(Other definitions for energy that I've seen before include "Vigour, animation" , "Zest" , "Exertion of force" , "Zeal" , "Healthy capacity for vigorous activity" .)