Unit of magnetic flux density (5)
I believe the answer is:
tesla
'unit of magnetic flux density' 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 "Inventive sort" , "Unit of magnetic flux density" , "Nikola ---, electricity pioneer" , "Californian company specialising in electric cars" , "SI unit; steal (anag.)" .)