German auto pioneer (4)
I believe the answer is:
benz
'german auto pioneer' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for benz that I've seen before include "German engineer who built the first petrol-engined car" , "German engineer, builder of first car with internal combustion engine" , "German pioneer of the internal-combustion engine, associated with Mercedes" , "Motor man" , "German engineer, first to build a patented car, d. 1929" .)