brother-in-law

[bruhth-er-in-law]

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.

brother-in-law

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

Word History and Origins

Origin of brother-in-law¹

First recorded in 1350–1400; Middle English brother in law(e); 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