From greasy spoon, a German stimulant (8)
I believe the answer is:
caffeine
'stimulant' is the definition.
(I've seen this before)
'from greasy spoon a german' is the wordplay.
I cannot really understand how this works, but
'from' could be 'in' (I've seen this in other clues) and 'in' is located in the answer.
'a' is within the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for caffeine that I've seen before include "Stimulant in, eg, cappuccino" , "Drug found in tea" , "coffee ingredient" , "Stimulating alkaloid" , "Stimulant found in mug or cup?" .)