The most common and most likely answer to this crossword clue is the 10 letter word SCEPTICISM
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More clues leading to the result SCEPTICISM
Buddy explains!

The straight part
We know that "doubt" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case doubt = scepticism.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 SCEPTICISM mean?
SCEPTICISM noun- The practice or philosophy of being a skeptic.
- A studied attitude of questioning and doubt
- The doctrine that absolute knowledge is not possible
- A methodology that starts from a neutral standpoint and aims to acquire certainty though scientific or logical observation.
- Doubt or disbelief of religious doctrines