The most common and most likely answer to this crossword clue is the 9 letter word INTERLACE
I've seen this crossword clue in The Daily Telegraph
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More clues leading to the result INTERLACE
Buddy explains!

The straight part
We know that "Ravel" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case ravel = interlace.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 INTERLACE mean?
INTERLACE noun- (visual arts) A decorative element found especially in early medieval art
- A technique of improving the picture quality of a video signal primarily on CRT devices without consuming extra bandwidth.
- To cross one with another.
- To mingle; to blend.
- To cross one another as if woven together; to intertwine; to blend intricately.