dimmer-switch

noun

1. a person or thing that dims.
2. Also called dimmer switch. a rheostat or similar device by which the intensity of an electric light may be varied.
3. dimmers,
   1. the low-beam headlights of an automobile or truck.
   2. the small, parking lights of an automobile.

noun

1. a device, such as a rheostat, for varying the current through an electric light and thus changing the illumination
2. (often plural) US
   1. a dipped headlight on a road vehicle
   2. a parking light on a car