n. (pl. -ies) 1 a belief or practice contrary to the orthodox doctrine of the Christian Church. b an instance of this. 2 a opinion contrary to what is normally accepted or maintained (it's heresy to suggest that instant coffee is as good as the real thing). b an instance of this. heresiology n.
[ ME f. OF (h)eresie, f. eccl.L haeresis, in L = school of thought, f. Gk hairesis choice, sect f. haireomai choose ]