Crossword Genius

Slimy oil substance (4)

Ross

I believe the answer is:

gunk

(Other definitions for gunk that I've seen before include "Unpleasantly sticky substance" , "Unpleasantly sticky stuff" , "Unpleasantly messy substance (informal)" , "Thick, sticky substance" , "Unpleasant sticky stuff" .)

I've seen this clue in The Guardian.
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