The most common and most likely answer to this crossword clue is the 8 letter word UNSEXING
U
N
S
E
X
I
N
G
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The straight part
We know that "castration" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case castration = unsexing.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 UNSEXING mean?
UNSEXING verb- To deprive of sexual attributes or characteristics.
- To sterilize (deprive of the ability to procreate); to castrate.