Substance in black lubricant put around (4)
I believe the answer is:
bulk
'substance' is the definition.
Although both the answer and definition are singular nouns, I cannot see how they can define each other.
'in black lubricant put around' is the wordplay.
'in' says the answer is hidden in the clue.
'around' says the letters should be written backwards.
'klub' can be found hidden inside 'black lubricant put'.
'klub' reversed gives 'BULK'.
Can you help me to learn more?
(Other definitions for bulk that I've seen before include "Mass (eg for buying)" , "Majority" , "Large mass; roughage" , "Mass of something large" , "Greater part" .)