0 having a more important job or position than someone else -- (役職が)上位の, 上級の
a senior executive
1 older -- 年上の
senior citizens
2 in the US, relating to a student’s fourth year of high school or college -- (高校または大学)4年生の
my senior year
3 in the US, a student in his or her fourth year of high school or college -- (高校または大学の)4年生
a group of graduating seniors
4 an older person, especially one who no longer works -- 高齢者
Entry is free for seniors.