(1):
(n.) An aged person; an older.
(2):
(n.) One in the fourth or final year of his collegiate course at an American college; - originally called senior sophister; also, one in the last year of the course at a professional schools or at a seminary.
(3):
(a.) Belonging to the final year of the regular course in American colleges, or in professional schools.
(4):
(a.) More advanced than another in age; prior in age; elder; hence, more advanced in dignity, rank, or office; superior; as, senior member; senior counsel.
(5):
(n.) A person who is older than another; one more advanced in life.
(6):
(n.) One older in office, or whose entrance upon office was anterior to that of another; one prior in grade.