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Meaning of holier-than-thou

ho•li•er-than-thou

Pronunciation: (hō'lē-ur-un-ou'), [key]
— adj.
  1. obnoxiously pious; sanctimonious; self-righteous.
—n.
  1. a person who is obnoxiously pious or self-righteous.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.