official
Coming from a person or group with real authority.
Official means coming from or approved by people in authority, making it legitimate and binding. When your principal announces an official snow day, school really is canceled. That is a decision you can rely on because it comes from someone with the authority to make it. When the referee makes an official call in a game, that decision stands, even if players disagree with it.
An official announcement carries weight because it comes from someone with the power to make decisions. Your teacher might mention that a field trip is being planned, but it's not official until the school sends home permission slips. The difference matters: official means you can count on it and act accordingly.
The word also describes people who hold positions of authority. Government officials run cities and countries. School officials include principals, superintendents, and school board members. These people have real responsibilities and the power to make decisions that affect others.
Sometimes official describes something formal and ceremonial, like an official state dinner or an official ceremony. In sports, the officials are the referees and umpires who enforce the rules. When something becomes official, it transforms from possibility to reality, from rumor to fact, from casual to binding.