The most common and most likely answer to this crossword clue is the 10 letter word EIGHTY-SIX
I've seen this crossword clue in The Guardian
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Buddy explains!

The straight part
We know that "Number" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case number = eighty-six.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.
Crossword Answer definitions
EIGHTY-SIX numeral- The cardinal number immediately following eighty-five and preceding eighty-seven.
- To cancel an order for food.
- To remove an item from the menu.
- To remove or eject, as a disruptive customer.
- To throw out; discard.