The most common and most likely answer to this crossword clue is the 9 letter word NARROWEST
I've seen this crossword clue in The Daily Telegraph
N
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More clues leading to the result NARROWEST
- Thinnest bolt has to fit inside casing
- Most restricted home gets object tipped inside
- Extremely strict lodge welcomes director
- Pointer in animal home thinner than the others
- Slightest quarrel occurs in breeding location
- Retreat admitting quarrel is most biased
- Pointer, in animal home, most restricted
- . Most provincial weapon in home
- Dart into the house, as access is extremely limited
- Most specific sign in bird's home
Buddy explains!

The straight part
We know that "most biased" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case most biased = narrowest.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 NARROWEST mean?
NARROWEST adjective- Having a small width; not wide; having opposite edges or sides that are close, especially by comparison to length or depth.
- Of little extent; very limited; circumscribed.
- Restrictive; without flexibility or latitude.
- Contracted; of limited scope; bigoted
- Having a small margin or degree.
- Limited as to means; straitened
- Parsimonious; niggardly; covetous; selfish.
- Scrutinizing in detail; close; accurate; exact.
- Formed (as a vowel) by a close position of some part of the tongue in relation to the palate; or (according to Bell) by a tense condition of the pharynx; distinguished from wide.