Contents of an old keg? (6)
I believe the answer is:
powder
'contents of an old keg?' is the definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Maybe you can see an association between them that I don't see?
This is the entire clue.
Can you help me to learn more?
(Other definitions for powder that I've seen before include "Small loose particles" , "Medical preparation" , "Solid that has been pulverised" , "Pulverise" , "Dust" .)