Mawson, C.O.S., ed. (1870–1938). Roget’s International Thesaurus. 1922.

Class VI. Words Relating to the Sentient and Moral Powers
Section V. Religious Affections
3. Religious Sentiments

988. Impiety.

   NOUN:IMPIETY; sin [See Vice]; irreverence; profaneness &c. adj., profanity, profanation; blasphemy, desecration, sacrilege; scoffing &c. v.
  [ASSUMED PIETY] hypocrisy &c. (false-hood) [See Falsehood]; pietism, cant, pious fraud; lip-devotion, lip-service, lip-reverence; misdevotion, formalism, austerity; sanctimony, sanctimoniousness &c. adj.; pharisaism, precisianism; sabbatism, sabbatarianism; odium theologicum [L.], sacerdotalism; bigotry (obstinacy) [See Obstinacy], (prejudice) [See Misjudgment]; blue laws.
  APOSTASY, recusancy, hardening, backsliding, declension, perversion, reprobation.
  HYPOCRITE (dissembler) [See Deceiver]; “Scribes and Pharisees” [Bible]; Rawana-sannyasi [Hind.]; Tartufe, Mawworm, Holy Willie [Burns].
  BIGOT, saint [ironical]; Pharisee, sabbatarian, formalist, methodist, puritan, pietist, precisian, religionist, devotee, ranter, fanatic; juramentado [Moro].
  SINNER [See Bad Man]; scoffer, blasphemer, sacrilegist [rare], sabbath breaker; worldling.
  the wicked, the evil, the unjust, the reprobate; sons of -men, – Belial, – the wicked one; children of -the devil, – darkness.
   VERB:BE IMPIOUS &c. adj.; profane, desecrate, blaspheme, revile, scoff; swear (malediction) [See Malediction]; commit sacrilege.
  DISSEMBLE, simulate, play the hypocrite, hypocrify [obs.], hypocrize [rare], snuffle, talk through the nose, talk nasally, hold up the hands in horror, turn up the whites of the eyes; sing psalms for a pretense, make long prayers.
   ADJECTIVE:IMPIOUS; irreligious [See Irreligion]; desecrating &c. v.; profane, irreverent, sacrilegious, blasphemous.
  unhallowed, unsanctified, unregenerate; hardened, perverted, reprobate.
  HYPOCRITICAL (false) [See Falsehood]; canting, pietistical, sanctimonious, unctuous, pharisaical, overrighteous, righteous over much.
  BIGOTED, fanatical, hidebound, narrow, illiberal, prejudiced, little; provincial, parochial, insular; priest-ridden.
   ADVERB:under the -mask, – cloak, – pretense, – form, – guise- of religion; in blasphemy.
  1. Giovane santo diavolo vecchio.
  2. Oh, for a forty-parson power to chant Thy praise, Hypocrisy!—Byron
  3. But all was false and hollow; though his tongue Dropped manna.—Paradise Lost
  4. O serpent heart, hid with a flowering face!—Romeo and Juliet
  5. Saint abroad, and a devil at home.—Bunyan