[ bruhth-er-in-law ]
/ ˈbrʌð ər ɪnˌlɔ /
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noun, plural broth·ers-in-law.

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



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Origin of brother-in-law

First recorded in 1350–1400; Middle English brother in law(e); see origin at brother, in, law1; 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
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2021

British Dictionary definitions for brother-in-law


noun plural brothers-in-law

the brother of one's wife or husband
the husband of one's sister
the husband of the sister of one's husband or wife
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
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