A in-law was a relative by marriage, as opposed to blood or adoption. The term was still in use in the late 24th century.
In 1947, Lieutenant General Denning of the United States Army Air Forces derogatorily remarked upon the similarity of Quark's behavior to that of his brother-in-law, a car salesman. (DS9: "Little Green Men")
In 2373, a Takarian sandal maker explained, when asked by Kol and Arridor why his shop was failing, that his mother-in-law was ill and his children were too young to work. (VOY: "False Profits")
While pondering his future as a potential Grand Nagus in 2375, Quark referred to Leeta as his lovely sister-in law. (DS9: "The Dogs of War")
In 2376, Reginald Barclay seemed surprised that Commander Harkins would approve of Barclay dating his sister-in-law Hope. He expressed his doubts about his worthiness as a "catch", citing his history of erratic behavior. (VOY: "Pathfinder")
List of in-laws
- Aurelan Kirk, sister-in-law of James T. Kirk
- George and Winona Kirk, parents-in-law of Aurelan Kirk
- Baron Grimes, father-in-law of Harcourt Fenton Mudd
- Ishka, mother-in-law of Leeta
- Owen Paris, father-in-law of B'Elanna Torres
- Owen Paris, father-in-law of Kes (alternate timeline)
- Tom Paris and Kes, parents-in-law of Harry Kim (alternate timeline)
- Marie Picard, sister-in-law of Jean-Luc Picard
- Quark, brother-in-law of Leeta
- Kyle Riker, father-in-law of Deanna Troi
- Joseph Sisko, father-in-law of Jennifer Sisko and Kasidy Yates
- Judith Sisko, sister-in-law of Jennifer Sisko and Kasidy Yates
- Lwaxana Troi, mother-in-law of William T. Riker