sister-in-law

American  

[sis-ter-in-law] / ˈsɪs tər ɪnˌlɔ /

noun

plural

sisters-in-law

1. the sister of one's spouse.

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

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

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sister-in-law British  

noun

1. the sister of one's husband or wife

2. the wife of one's brother

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Etymology

Origin of sister-in-law

First recorded in 1400–50; late Middle English syster in lawe; see origin at sister, 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

The patient’s sister-in-law told them a nurse practitioner “came to the home a few times to treat J.L.’s flesh infection and “did not treat the open wounds often because they were too infected.”

From Los Angeles Times • Apr. 28, 2026

The brother and sister-in-law of the late Virginia Giuffre also echoed the call in an interview with the BBC's Newsnight programme.

From BBC • Apr. 26, 2026

I didn’t fully become One with a ring until this January when my extremely fit, pickleball-playing sister-in-law bowed out one morning from a family hike at the urging of her ring.

From The Wall Street Journal • Mar. 29, 2026

James Ridgway and his sister-in-law Eleanor Brown, who set up the Brew 32 café in Stockport last year, says they've noticed the shift.

From BBC • Mar. 23, 2026

Frear got across the river “after a severe struggle, and at the risk of my life” and continued his search for his sister-in-law and Wood.

From "The Great Fire" by Jim Murphy

Related Words

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