What is the meaning of brotherhood?

noun

• The kinship relation between a male offspring and the siblings.
• People engaged in a particular occupation.
  • usage: "the medical fraternity"
  • synonyms: fraternity, sodality
• The feeling that men should treat one another like brothers.
• An organization of employees formed to bargain with the employer.
  • usage: "you have to join the union in order to get a job"
  • synonyms: union, labor union, trade union, trades union