Unit in current use (6)
I believe the answer is:
ampere
'unit' is the definition.
(I know that ampere is a type of electromagnetic unit)
'current use' is the wordplay.
'current' becomes 'amp' (electricity).
'use' becomes 'ere' (I can't explain this - if you can you should give a lot more credence to this answer).
'amp'+'ere'='AMPERE'
'in' is the link.
Can you help me to learn more?
(Other definitions for ampere that I've seen before include "Current measure" , "Unit of currency" , "Solenoid inventor" , "Unit of electrical current" , "Basic SI unit of electric current" .)