The most common and most likely answer to this crossword clue is the 9 letter word KADAITCHA
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More clues leading to the result KADAITCHA
Buddy explains!

The straight part
We know that "One avenging" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case one avenging = kadaitcha.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 KADAITCHA mean?
KADAITCHA noun- An aboriginal evil spirit; a sorcerer.
- An expedition taken to heal or avenge someone afflicted by evil sorcery.
- A man chosen to go on such an expedition.
- The boots worn by someone on such a mission, typically made from emu feathers.