Brethren is an old-fashioned or formal word meaning brothers, or more broadly, fellow members of a group who share something important like faith, purpose, or profession.

You might encounter brethren in historical documents, religious texts, or traditional ceremonies. A minister addressing a congregation might say “Brothers and sisters” in modern English, but in older times might have said “Brethren.” Members of some religious orders still use brethren to emphasize their spiritual bond as a kind of family.

The word carries a feeling of deep connection and shared commitment. When firefighters or soldiers call each other brethren, they're recognizing that they face dangers together and depend on each other completely. It suggests something stronger than just friends or colleagues: people who are bound together by loyalty, shared values, or a common purpose.

Today, brethren sounds formal or old-timey in everyday conversation. You'd say “my brothers” or “my fellow students” rather than “my brethren.” But the word still appears in speeches, ceremonies, or writing that aims for a serious, elevated tone. Some organizations, like certain religious groups, specifically call themselves “Brethren” as part of their name, emphasizing their view of membership as creating family-like bonds.