The most common and most likely answer to this crossword clue is the 8 letter word HACKLING
I've seen this crossword clue in Independent
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The straight part
We know that "Using a comb/challenging" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case using a comb/challenging = hackling.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 HACKLING mean?
HACKLING verb- To dress (flax or hemp) with a hackle; to prepare fibres of flax or hemp for spinning.
- To separate, as the coarse part of flax or hemp from the fine, by drawing it through the teeth of a hackle or hatchel.
- To tear asunder; to break into pieces.