Infrared

How to spell infrared

8 letters · 3 syllables

How to pronounce infrared

Say the part in capitals loudest.

What does infrared mean?

1. adjectiveRelating to electromagnetic radiation with wavelengths longer than visible red light, often felt as heat and used in remote sensing.
2. nounInvisible radiation lying just beyond the red end of the visible spectrum.

Infrared in a sentence

• adjective

  The security system uses infrared sensors to detect movement in the dark.

• noun

  The remote control sends its signal using infrared rather than radio waves.

• adjective

  The new oven cooks faster using infrared heating elements.

• noun

  Astronomers study cool, dusty regions of space by observing in the infrared.

Where does infrared come from?

Language of origin: Latin

This word is a scientific compound coined in English, joining the Latin prefix infra-, which literally means 'below' or 'beneath', to the ordinary colour word 'red'. The naming reflects real physics: infrared radiation sits just 'below' red on the spectrum, meaning its waves are longer and its frequency lower than the reddest light the human eye can see. The phenomenon was discovered around 1800 by the astronomer William Herschel, who measured a rise in temperature beyond the red end of a sunlit spectrum and realised an invisible form of radiation lay there. The hyphenated form 'infra-red' was used through the nineteenth century before settling into the single closed word we use today. Because the prefix is the unfamiliar part, the spelling trap is remembering it is infra-, not 'inter-' or 'infer-', and that the word ends in the plain, familiar 'red'.

How the word is built

• infra- (below, beneath)
• red (the colour at the long-wavelength edge of visible light)