three-way switch
nounEtymology Named after its three electrical connections, as opposed to the two connections of a normal light switch.
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Business, Electrical engineering, Electricity, Electromagnetism, Energy, Engineering, Natural sciences, Physical sciences, Physics US A type of light switch that can be arranged in pairs to control lights from two locations, as at either end of a stairway or long hallway; a double-throw switch. (UK): two-way switch.