Senior describes someone or something that ranks higher, has more experience, or came first. In some schools, seniors are students in their final year, such as twelfth grade in high school. These students have been at their school longer than anyone else in their grade, which often gives them special privileges and responsibilities.

In the workplace, a senior engineer or senior manager has more experience and authority than newer employees. They've proven their skills over time and often guide less experienced workers. Your grandfather might be a senior citizen, which usually means someone over 65, recognizing that older people have lived longer and accumulated more life experience.

When you see “Jr.” after someone's name (like Martin Luther King Jr.), it means “junior,” marking them as the younger of two people with the same name. The older person might use “Sr.” for “senior.”

You might also hear seniority used to describe the advantage that comes from being somewhere longer. In a family business, the senior partner founded the company, while newer partners joined later. Being senior usually means others look to you for leadership and wisdom, whether you're the oldest cousin at a family reunion or the veteran player on a sports team showing newcomers how things work.