The most common and most likely answer to this crossword clue is the 8 letter word RIDDANCE
I've seen this crossword clue in Independent
R
I
D
D
A
N
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E
Buddy explains!

The straight part
We know that "clearance" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case clearance = riddance.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 RIDDANCE mean?
RIDDANCE noun- The act of being rid of something; deliverance
- The earth thrown up by a burrowing animal.