adjective

1. of the greater age; older: written Sr. after the name of a father whose son has been given exactly the same name
2. of higher rank or standing, or longer in service
3. ☆ of or for seniors in a high school or college
4. of or for senior citizens senior athletes, a senior center

Etymology: ME < L senior, compar. of senex, old: see senate

noun

1. a person older than another or others
2. a person of greater rank, standing, or length of service
3. ☆ a student in the last year of college or the twelfth grade in high school
4. senior citizen