brother in WordNet English dictionary

1. a male with the same parents as someone else
   "my brother still lives with our parents"
   brother  blood brother 
   
2. a male person who is a fellow member (of a fraternity or religion or other group)
   "none of his brothers would betray him"
   brother 
   
3. a close friend who accompanies his buddies in their activities
   buddy  brother  chum  crony  pal  sidekick 
   
4. used as a term of address for those male persons engaged in the same movement
   "Greetings, comrade!"
   brother  comrade