Inventor Nikola (5)
I believe the answer is:
tesla
'inventor nikola' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for tesla that I've seen before include "Californian company specialising in electric cars" , "Inventor" , "Nikola ---, electricity pioneer" , "Physics unit" , "Unit of magnetic flux density" .)