a boy or man who has the same parents as another person

used for talking to or talking about other male members of an organization or other men who have the same ideas, purpose, etc. as yourself

We are all brothers in the fight against injustice.

He was greatly respected by his brother officers.

We must support our weaker brethren.

a male member of a religious group, especially a monk

The Brethren meet regularly for prayer.

used by black people as a form of address for a black man

(in the US) a member of a fraternity(= a club for a group of male students at a college or university)

used to express the fact that you are annoyed or surprised

LEARNit Dictionary