contrary to mainstream or accepted opinion; (especially views contrary to established teachings of the Roman Catholic church) but also contrary to other denominations
A belief or action that is heretical is one that seriously disagrees with the principles of a particular religion. The Church regards spirit mediums and people claiming to speak to the dead as heretical
A belief or action that is heretical is one that most people think is wrong because it disagrees with beliefs that are generally accepted. I made the then heretical suggestion that it might be cheaper to design new machines