The most common and most likely answer to this crossword clue is the 7 letter word SOPHIST
I've seen this crossword clue in Independent
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More clues leading to the result SOPHIST
Buddy explains!
The straight part
We know that "one who’ll split hairs?" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case one who’ll split hairs? = sophist.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 SOPHIST mean?
SOPHIST noun- One of a class of teachers of rhetoric, philosophy, and politics in ancient Greece.
- A teacher who used plausible but fallacious reasoning.
- (by extension) One who is captious, fallacious, or deceptive in argument.
- A sophist.
- (universities) A student who is advanced beyond the first year of their residence.