encender
/enθenˈdeɾ/ · A2 · verb
to turn on, switch on, power up
🔥💡 en + cender: Latin incendere, to set on fire — same root as incendiary
From Latin incendere (to set ablaze), which also gave English incendiary and incense. Fire came first; switching on a lamp or a device is the modern extension, so you still encender la luz. Opposite: apagar.