brother-in-law

• brother in law

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

• (General American) IPA^(key): /ˈbɹʌðɚ ɪn ˌlɔ/
• (cot–caught merger, Canada) IPA^(key): /ˈbɹʌðɚ ɪn ˌlɑ/
• (Received Pronunciation) IPA^(key): /ˈbɹʌðəɹ ɪn ˌlɔː/

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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’)”, in 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.

• c. 1597 (date written), William Shakespeare, “The First Part of Henry the Fourth, […]”, in Mr. William Shakespeares Comedies, Histories, & Tragedies […] (First Folio), London: […] Isaac Iaggard, and Ed[ward] Blount, published 1623, →OCLC, [Act I, scene iii]:

  We at our own charge shall ransom straight
  His brother-in-law, the foolish Mortimer;

• “brother-in-law”, in Webster’s Revised Unabridged Dictionary, Springfield, Mass.: G. & C. Merriam, 1913, →OCLC.
• “brother-in-law”, in Dictionary.com Unabridged, Dictionary.com, LLC, 1995–present.
• "brother-in-law" in Cambridge Advanced Learner's Dictionary (Cambridge University Press, 2007)
• Random House Webster's Unabridged Electronic Dictionary (1987-1996)