Definition of infrared
1
: situated outside the visible spectrum at its red end
—used of radiation having a wavelength between about 700 nanometers and 1 millimeter
2
: relating to, producing, or employing infrared radiation
infrared therapy
3
: sensitive to infrared radiation
infrared sensors that detect body heat
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Merriam-Webster unabridged
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Time Traveler for infrared
The first known use of infrared was in 1881
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