sanc·ti·mo·ni·ous (sāngk'tə-mō'nē-əs) adj. Feigning piety or righteousness: "a solemn, unsmiling, sanctimonious old iceberg that looked like he was waiting for a vacancy in the Trinity"(Mark Twain). sanc'ti·mo'ni·ous·ly adv., sanc'ti·mo'ni·ous·ness n.
1603 (in "Measure for Measure," with the disparaging sense), from sanctimony "holiness of life and character" (1540), from M.Fr. sanctimonie, from L. sanctimonia "holiness, virtuousness," from sanctus "holy" (see saint). The un-ironic, literal sense was used occasionally in Eng. from 1604 to c.1800.