Definition of "Brother" :

noun: a male with the same parents as someone else

"My brother still lives with our parents."

noun: (Roman Catholic Church) a title given to a monk and used as form of address

"A Benedictine Brother."

noun: a male person who is a fellow member (of a fraternity or religion or other group)

"None of his brothers would betray him."

noun: used as a term of address for those male persons engaged in the same movement

noun: a close friend who accompanies his buddies in their activities