The most common and most likely answer to this crossword clue is the 8 letter word VERACITY
I've seen this crossword clue in The Daily Telegraph
V
E
R
A
C
I
T
Y
Buddy explains!
The straight part
We know that "Truth" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case truth = veracity.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 VERACITY mean?
VERACITY noun- (of a person) The quality of speaking or stating the truth; truthfulness.
- Something that is true; a truthful statement; a truth.
- Agreement with the facts; accordance with the truth; accuracy or precision.
- Act of being exact and accurate.
- Correctness and carefulness in one's plan of action.