senior

from The Century Dictionary.

• Older; elder: when following a personal name, as John Smith, senior (usually abbreviated Sr. or Sen.), it denotes the older of two persons in one family or community of that name.
• 2. Older in office or service: as, a senior judge, colonel, etc.
• 3. Belonging or pertaining to the fourth or last year of the curriculum of an American college, seminary, or other institution: as, the senior class.
• noun A person who is older than another; one more advanced in life; an elder.
• noun One who is older in office or service, or whose first entrance upon such office or service was anterior to that of another.
• noun 3. An aged person; one of the older inhabitants.
• noun In the universities of England, one of the older fellows of a college. See seniority, 3.
• noun In the United States, a student in the fourth year of the curriculum in colleges or seminaries; also, one in the last or most advanced year in certain professional schools; by extension, a student in the most advanced class in various institutions.

from the GNU version of the Collaborative International Dictionary of English.

• adjective More advanced than another in age; prior in age; elder; hence, more advanced in dignity, rank, or office; superior.
• adjective Belonging to the final year of the regular course in American colleges, or in professional schools.
• noun A person who is older than another; one more advanced in life.
• noun One older in office, or whose entrance upon office was anterior to that of another; one prior in grade.
• noun An aged person; an older.
• noun 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.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• adjective Older; superior
• adjective Higher in rank within a publicly traded company or other organization.
• adjective of or pertaining to a student's final academic year at a high school (twelfth grade) or university.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun an undergraduate student during the year preceding graduation
• adjective older; higher in rank; longer in length of tenure or service
• adjective advanced in years; (`aged' is pronounced as two syllables)
• adjective used of the fourth and final year in United States high school or college
• noun a person who is older than you are