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.