Definition of "heresy"

heresy

/ˈhɛɹəsi/

noun
countable and uncountable, plural heresies
1. (religion) a doctrine held by a member of a religion at variance with established religious beliefs
  Quotations
  Heresy meant deliberate departure from the accepted doctrines of the church. It was intellectual and spiritual dissent and concerned the beliefs of Christianity, not the morals of its adherents.
  1968, History of Western Civilization, edited by Heyes, Baldwin & Cole, p.47. Macmillan. Library of Congress 67–13596
2. (by extension) A controversial or unorthodox opinion held by a member of a group, as in politics, philosophy or science.
  Quotations
  I'm going to declare a heresy for you. All science, if you go back into its roots, saying: 'Why do I believe this?' 'Well, I believe this because of these tests and this proof.' 'Well, why do I believe this?' 'Why did I set up this test?' 'Why did I believe that proof?' All science goes back to something that we believe because we believe it. We believe it because we believe it, and we have no proof for it. It's like a religion.
  1985 April 17, Frank Herbert, 15:58 from the start, in Frank Herbert speaking at UCLA 4/17/1985‎, UCLACommStudies, archived from the original on 10 February 2017