From BiblePortal Wikipedia

Webster's Dictionary [1]

(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.

Cyclopedia of Biblical, Theological and Ecclesiastical Literature [2]

(1), a monk from the age of forty to fifty years who was excused from the external offices of provisor, procurator, cellarer, almoner, kitchener, master of the works, etc., but took his turn in singing masses. (2) The head of a college of secular calons, as at Christ-church, Hants, 1099. (3) At Osnaburg, Trent, L beck, and in some Italian cathedrals, the antianus, or senior, corresponds to the archpriest of certain French cathedrals, in which he acted in the bishop's absence as his representative in the administration of sacraments and the benediction of ashes, palms, and the font. Such an archpriest was required in every cathedral by the Council of Merida.