in-law

American  

[in-law] / ˈɪnˌlɔ /

noun

1. a relative by marriage.

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in-law British  

noun

1. a relative by marriage

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adjective

1. (postpositive; in combination) related by marriage

   a father-in-law

Etymology

Origin of in-law

First recorded in 1890–95; back formation from mother-in-law, brother-in-law, etc.

Explanation

An in-law is someone who is a relative because of marriage, like your husband's sister or your wife's father. You can refer to your spouse's entire family as your in-laws. In some countries, a married woman moves in with her in-laws, symbolically becoming part of their family. In the U.S. some families live with extended family members — a man may live with his wife, kids, and his mother- and father-in-law — but more often each individual nuclear family lives separately. In-law originally meant "anyone of a relationship not natural" or "not by blood."

Example Sentences

There’s also a lower-level lounge, media room, wine cellar, an in-law suite, and a home gym.

From MarketWatch • Nov. 26, 2025

The presence of the surly uncle, insufferable in-law, or grating girlfriend at the holiday table can make it hard to truly count one’s blessings.

From The Wall Street Journal • Nov. 21, 2025

She might be your aunt or an in-law.

From Salon • Oct. 16, 2025

The Lebanese American businessman is the second in-law to be offered a position in the incoming administration, after Trump picked Charles Kushner, his daughter Ivanka’s father-in-law, to serve as ambassador to France.

From BBC • Dec. 2, 2024

Judging from the layout, the second floor space had probably been designed as an in-law apartment meant for one or two people, but four of us found a way to fit inside.

From "Becoming" by Michelle Obama