a. [ Infra- + red. ] 1. (Physics) Lying outside the visible spectrum at its red end; -- said of rays having a longer wavelength (and thus less refrangible) than the extreme red rays, specifically those electromagnetic waves having a wavelength of between 700 nanometers and 1 millimeter. [ Webster 1913 Suppl. +PJC ]

2. relating to, using, or producing infrared radiation. [ PJC ]

3. affected by infrared radiation; as, infrared detector; infrared film. [ PJC ]