fraternity

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A body of people associated for a common purpose or interest, such as a guild.
• noun A group of people joined by similar backgrounds, occupations, interests, or tastes.
• noun A social organization at a college or university, traditionally consisting of male students and designated by Greek letters.
• noun Roman Catholic Church A sodality.
• noun The quality or condition of being brothers; brotherliness.

from The Century Dictionary.

• noun The relationship of a brother; the condition of being a brother or of being brothers; brotherhood.
• noun Hence That mutual interest and affection which is characteristic of the fraternal relation; brotherly regard and sympathy for others, regardless of relationship by blood; brotherhood in general.
• noun A body of men associated by some natural tie, as of common interest or character, of common business or profession, or by some formal tie, as of organization for religious or social purposes; a company; a brotherhood; a society: as, a fraternity of monks; a college fraternity.
• noun Specifically, in the Roman Catholic Church, an organization of laymen for pious or charitable purposes, as the special worship of Christ, the honor of the Virgin Mary or of particular saints, the care of the distressed, sick, or dead, etc. Also called confraternity, gild, or sodality.

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

• noun The state or quality of being fraternal or brotherly; brotherhood.
• noun A body of men associated for their common interest, business, or pleasure; a company; a brotherhood; a society; in the Roman Catholic Church, an association for special religious purposes, for relieving the sick and destitute, etc.
• noun Men of the same class, profession, occupation, character, or tastes.
• noun A social club for male college undergraduates. They often have secret initiation rites, and are named by the use of two or three Greek letters. The corresponding association for women students is called a sorority.

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

• noun The quality of being brothers; brotherhood
• noun A group of people associated for a common purpose.
• noun US A social organization of male students at a college or university; usually identified by Greek letters.

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

• noun a social club for male undergraduates
• noun people engaged in a particular occupation