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See also: brother in law


Alternative forms[edit]


From Middle English brother-in-lawe; equivalent to brother +‎ -in-law.



brother-in-law (plural brothers-in-law or (archaic) brethren-in-law or (colloquial, nonstandard) brother-in-laws)

  1. A male relative of one's generation, separated by one degree of marriage:
    1. The brother of one's spouse.
    2. The husband of one's sibling.
  2. (uncommon) Co-brother-in-law: A male relative of one's generation, separated by two degrees of marriage:
    1. The husband of the sibling of one's spouse.
      • 2009 Donal Lowry, "Kettle, Thomas Michael (‘Tom’)", Dictionary of Irish Biography (Cambridge University Press)
        He was appalled by trench conditions and the prolongation of the war, a disillusionment further encouraged by the Easter rising, in which his brother-in-law, Francis Sheehy-Skeffington (qv), was murdered by a deranged Anglo-Irish officer, J. C. Bowen-Colthurst (qv).
    2. The brother of the spouse of one's sibling.


  • 1597, William Shakespeare, Henry IV, Part I, act 1, sc. 3,
    We at our own charge shall ransom straight
    His brother-in-law, the foolish Mortimer;

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