The most common and most likely answer to this crossword clue is the 9 letter word OUROBOROS
I've seen this crossword clue in Independent
O
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Buddy explains!
The straight part
We know that "Boa devouring tail, or so our representation shows" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case boa devouring tail, or so our representation shows = ouroboros.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 OUROBOROS mean?
OUROBOROS noun- A serpent, dragon or worm that eats its own tail, a representation of the continuous cycle of life and death.
- A picture or symbol representing the first definition.