brother-in-law

American  

[bruhth-er-in-law] / ˈbrʌð ər ɪnˌlɔ /

noun

brothers-in-law plural

1. the brother of one's spouse.

2. the husband of one's sister or brother.

3. the husband of one's spouse's sister or brother.

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brother-in-law British  

noun

1. the brother of one's wife or husband

2. the husband of one's sister

3. the husband of the sister of one's husband or wife

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Other Word Forms

Noun Inflected Forms

• brothers-in-law
  plural

Etymology

Origin of brother-in-law

First recorded in 1350–1400; Middle English brother in law(e); see origin at brother, in, law ¹; from Middle English in-lawe “in law,” i.e., “a person within the regulation and protection of the law,” based on the prohibition by Roman civil law and, later, Christian canon law, of marriages within four degrees of consanguinity, i.e., up to and including first cousins

Example Sentences

At the hospital outside General Santos, Lourdes Camia said she believed her brother-in-law, who was being treated for a heart attack, was safer outside -- despite the heat.

From Barron's • Jun. 9, 2026

The Princess of Wales's brother-in-law has told a planning inquiry his family home needs a higher level of security in a row over part of its drive being designated a public footpath.

From BBC • May 28, 2026

At one point, Spaeny looked over to see her brother-in-law having a heart-to-heart with Melton’s dad.

From Los Angeles Times • May 27, 2026

Helping his brother-in-law film a documentary, Thapar watched as their subject stalked a herd of sambar deer in one of the many Ranthambore lakes.

From The Wall Street Journal • Apr. 21, 2026

Jimmy’s brother-in-law was the director of the Newsome Park Community Center.

From "Hidden Figures" by Margot Lee Shetterly

Related Words

• aunt
• cousin
• father
• folk
• mother
• niece
• sibling
• uncle