Senior \Sen"ior\, a. [L. senior, compar. of senex, gen. senis, old. See Sir.]

1. More advanced than another in age; prior in age; elder; hence, more advanced in dignity, rank, or office; superior; as, senior member; senior counsel.

2. Belonging to the final year of the regular course in American colleges, or in professional schools.

Source: Webster's Revised Unabridged Dictionary (1913)
 

Senior \Sen"ior\, n.

1. A person who is older than another; one more advanced in life.

2. One older in office, or whose entrance upon office was anterior to that of another; one prior in grade.

3. An aged person; an older. --Dryden.

Each village senior paused to scan, And speak the lovely caravan. --Emerson.

4. 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.

Source: Webster's Revised Unabridged Dictionary (1913)