The most common and most likely answer to this crossword clue is the 9 letter word MENDACITY
I've seen this crossword clue in The Times
M
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D
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More clues leading to the result MENDACITY
- Lying to get candy item changed
- Undertake urban regeneration programme? Fraudulent practice
- Many cited terrible untruthfulness
- Telling fibs, incorrectly named Liverpool?
- Carry out urban repairs with crooked quality
- Lying urban reformer’s promise may be this
- Improve a financial centre’s dishonesty
- Lying urban reformer’s slogan?
- Fellows not only committing robbery, also showing deceit
- Deceit to get a financial centre working again
Buddy explains!

The straight part
We know that "untruthfulness" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case untruthfulness = mendacity.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 MENDACITY mean?
MENDACITY noun- The fact or condition of being untruthful; dishonesty.
- A deceit, falsehood, or lie.