Crossword Genius

Struggles to take top off paint (4)

Ross

I believe the answer is:

oils

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'paint' is the definition.
(thesaurus)

I don't understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for oils that I've seen before include "Viscous substances kept in silo" , "Lubricates; paints" , "Reduces friction" , "art exhibits perhaps" , "Lubricants stored in silo" .)

I've seen this clue in The Guardian.
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