The most common and most likely answer to this crossword clue is the 8 letter word DEVIANCE
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The straight part
We know that "abnormality" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case abnormality = deviance.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 DEVIANCE mean?
DEVIANCE noun- Actions or behaviors that violate formal and informal cultural norms such as laws and customs.
- A person or thing that differs from the expected.