Something which cannot be tampered with, or criticized, for fear of public outcry. A person, institution, belief system, etc. which, for no reason other than the demands of established social etiquette or popular opinion, should be accorded respect or reverence, and not touched, handled or examined too closely
disapproval If you describe a belief, custom, or institution as a sacred cow, you disapprove of people treating it with too much respect and being afraid to criticize or question it. the sacred cow of monetarism. One that is immune from criticism, often unreasonably so: "The need for widespread secrecy has become a sacred cow" (Bulletin of the Atomic Scientists). a belief, custom, system etc that is so important to some people that they will not let anyone criticize it