The most common and most likely answer to this crossword clue is the 9 letter word LUBRICANT
I've seen this crossword clue in Financial Times
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More clues leading to the result LUBRICANT
- It’s used to smear notorious Earl entangled with British citizen
- Train club in new way that makes things go more smoothly
- Oil spill in Cuba ends in all out war
- Setter’s unable to bear hints of lactose used by restaurants as sweetener
- Vigorously rub in talc, overcoming friction
- Oil from car, until changed, black inside
Buddy explains!

The straight part
We know that "It/’s used to smear" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case it/’s used to smear = lubricant.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does LUBRICANT mean?
LUBRICANT noun- A substance used to reduce friction between objects or surfaces.
- A personal lubricant.