Just one is not very electrifying (4)
I believe the answer is:
volt
'just one' is the definition.
The answer and definition can be both quantities as well as being singular nouns.
Maybe you can see an association between them that I don't see?
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for volt that I've seen before include "Electrical SI unit named after a pioneering Italian physicist, d. 1827" , "SI unit of electromotive force" , "Unit of electric force" , "Electricity unit" , "Electrical unit of measurement" .)