When someone is sanctimonious, they act like they are morally better than other people, but they are not really better.
Being sanctimonious is not good because it usually means someone is pretending to be good.
Examples:
She is always saying how good she is, but I think she is just being sanctimonious.
I don't like his sanctimonious attitude.
He acts sanctimonious, but I know he is not really that good.
The sanctimonious lady always talks about how much she helps people, but I never see her doing anything.
His sanctimonious behavior makes me feel like he is not honest.
The sanctimonious man thinks he is better than everyone else, but he is not.