Scottish inventor (4)
I believe the answer is:
watt
'scottish inventor' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for watt that I've seen before include "Engineer, coined the term horsepower, d. 1819" , "Light bulb unit" , "bit of power" , "Worker in steam" , "Unit of power -- Scottish engineer, d. 1819" .)