"The formal denial or doubt of any defined doctrine of the Catholic faith. In antiquity the Greek word αἵρεσις, denoting ‘choice’ or ‘thing chosen’, from which the term is derived, was applied to the tenets of particular philosophical schools. In this sense it appears occasionally in Scripture (e.g. Acts 5: 17) and the early Fathers. But it was employed also in a disparaging sense (e.g. 1 Cor. 11: 19) and from St Ignatius (Trall. 6, Eph. 6) onwards it came more and more to be used of theological error. . . ."
"heresy" The Oxford Dictionary of the Christian Church. Ed. F. L. Cross and E. A. Livingstone. © Oxford University Press 2005. The Oxford Dictionary of the Christian Church: (e-reference edition). Oxford University Press. Seattle Pacific University. 4 June 2012 http://ezproxy.spu.edu/login?url=http://www.oxford-christianchurch.com/entry?entry=t257.e3211.