The most common and most likely answer to this crossword clue is the 9 letter word SUSPECTED
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The straight part
We know that "Mistrusted" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case mistrusted = suspected.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 SUSPECTED mean?
SUSPECTED verb- To imagine or suppose (something) to be true, or to exist, without proof.
- To distrust or have doubts about (something or someone).
- To believe (someone) to be guilty.
- To have suspicion.
- To look up to; to respect.
- Believed to be a cause or at fault.