Dimmer
WordNet
noun
(1) A rheostat that varies the current through an electric light in order to control the level of illumination
WiktionaryText
Noun
- A rheostat that is used to vary the intensity of a domestic electric light
- A switch used to select between the low and high headlamp beam on a road vehicle. (usually as "dimmer switch", primarily in North America; elsewhere "dipswitch" or "dipper switch")