To darken means to make something less bright or to become less bright. When you darken a room, you might close the curtains, dim the lights, or turn them off completely. The sky darkens as the sun sets, gradually shifting from bright blue to deep purple and finally to black.

The word also describes making colors deeper or more intense. An artist might darken a shade of blue by adding black paint to it. A piece of wood darkens over time as it ages, or you can darken it faster by applying stain.

Darken can describe moods and expressions too. When someone's face darkens, their expression becomes more serious, worried, or angry. You might notice a teacher's expression darken when students aren't paying attention, or see a friend's mood darken after hearing disappointing news.

The word suggests a gradual change rather than an instant switch. A room doesn't usually darken all at once unless you flip off the lights. More often, it darkens slowly as evening approaches, giving your eyes time to adjust. When storm clouds gather and darken the afternoon sky, they build up gradually before the rain arrives.