The most common and most likely answer to this crossword clue is the 9 letter word LAMBSWOOL
I've seen this crossword clue in The Guardian
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More clues leading to the result LAMBSWOOL
Buddy explains!
The straight part
We know that "natural fibre" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case natural fibre = lambswool.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 LAMBSWOOL mean?
LAMBSWOOL noun- Wool from a lamb.
- (by extension) Something made of wool from a lamb.
- A festive drink of ale mixed with the pulp of roasted apples.