- For or between three parties. Often used in reference to alliances.
- 2014, Naomi Wood, Mrs. Hemingway, →ISBN:
- Everything, now, is done à trois.
- 2015, Elizabeth Jeffrey, Meadowlands, →ISBN:
- In the event Lady Adelaide looked rather overdressed for an informal dinner à trois.
- 2016, From Sadowa to Sarajevo, volume 6, →ISBN:
- Nor, he warned, would he have anything to do with an agreement à trois with Russia.
- A discussion à trois.
- à trois in a Europe of five powers(= being allied with three of the five main powers)