éteindre

The French verb « éteindre » means "to turn off" or "to extinguish". It is most commonly used for:

• Turning off electrical devices (lights, appliances):
  éteindre la lumière – turn off the light
• Extinguishing fires or flames:
  éteindre un feu – put out a fire
• Also used figuratively, for example to "quench" feelings or sounds:
  éteindre une émotion – suppress/quiet an emotion

Synonyms and their nuances:

• arrêter: means "to stop" broadly (a machine, a vehicle, a process), but not usually used to mean putting out a fire or turning off a light.
  Example: arrêter la voiture – stop the car

• couper: means "to cut" or "cut off," often used with electricity or water supply (e.g., couper le courant), but less common directly for turning off lights.
  Example: couper l'électricité – cut off the electricity

• débrancher: specifically means "to unplug" a device from its power source to turn it off, whereas éteindre only means switching off, not unplugging.

In summary, « éteindre » is the precise verb to use when talking about switching off lights or machines and extinguishing fires or flames.