Fuel — the German variety, originally (4)
I believe the answer is:
derv
'fuel' is the definition.
(derv is a kind of fuel)
'the german variety originally' is the wordplay.
'the german' becomes 'der' ('the' in German).
'originally' says to take the initial letters.
The first letter of 'variety' is 'v'.
'der'+'v'='DERV'
(Other definitions for derv that I've seen before include "Diesel engine fuel oil" , "Vehicle fuel oil" , "Type of fuel" , "Fuel for lorries" , "Lorry fuel" .)