A belief or conclusion held with confidence but not substantiated by positive knowledge or proof: "The world is not run by thought, nor by imagination, but by opinion\u201d ( Elizabeth Drew). A judgment based on special knowledge and given by an expert: a medical opinion. A judgment or estimation of the merit of a person or thing: has a low opinion of braggarts. The prevailing view: public opinion. Law A formal statement by a court or other adjudicative body of the legal reasons and principles for the conclusions of the court.