Broth"er-in-law` (&?;), n.; pl. Brothers-in-law (&?;). The brother of one's husband or wife; also, the husband of one's sister; sometimes, the husband of one's wife's sister.

• a brother of someone's husband
  
• a brother of someone's wife
  
• the husband of someone's sister
  
• the husband of the sister of someone's husband
  
• the husband of the sister of someone's wife