Truthfulness occasionally heard in Vegas, for example (9)
I believe the answer is:
sincerity
'truthfulness' is the definition.
(sincerity is a kind of truthfulness)
'occasionally heard in vegas for example' is the wordplay.
I cannot quite understand how this works, but
'in' is within the answer.
This may be the basis of clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for sincerity that I've seen before include "truth" , "Straightforwardness" , "Openness and truthfulness" , "Genuineness" .)