Synonyms for Infrared (same or very similar meaning)
WordNet sense 1 (electromagnetic radiation with wavelengths longer than visible light but shorter than radio waves):
infrared emission, infrared light, infrared radiation
WordNet sense 2 (the infrared region of the electromagnetic spectrum; electromagnetic wave frequencies below the visible range):
infrared frequency
WordNet sense 3 (impossible or nearly impossible to see; imperceptible by the eye):
invisible, unseeable
From the ODE community, based on WordNet
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