brother-in-law

American  

[bruhth-er-in-law] / ˈbrʌð ər ɪnˌlɔ /

noun

plural

brothers-in-law

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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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

Related Words

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