Definition of halogen in US English:



  • 1Any of the elements fluorine, chlorine, bromine, iodine, and astatine, occupying group VIIA (17) of the periodic table. They are reactive nonmetallic elements that form strongly acidic compounds with hydrogen from which simple salts can be made.

    • ‘Four important chemical family names of elements still widely used are the alkali metals, the alkaline earths, the halogens, and the noble gases.’
    • ‘The oxidation number of the halogens other than fluorine is - 1, unless they are bonded to oxygen or a more electronegative halogen.’
    • ‘Metals high on the activity series react more vigorously with oxidants including the halogens and the hydronium ion than those lower on the scale.’
    • ‘Silicon behaves somewhat similarly to carbon, but compounds of silicon and hydrogen or silicon and the halogens (the silanes) are much more reactive than their carbon counterparts.’
    • ‘For many syntheses, this means using such compounds as hydrocarbons and alcohols, plus inorganic acids, metals, halogens, or other compounds.’
    1. 1.1as modifier Denoting lamps and radiant heat sources using a filament surrounded by the vapor of iodine or another halogen.
      ‘halogen headlights’
      • ‘The light source was a microscope halogen lamp, which unilaterally illuminated the protruding stump, via a light guide at a site 2-4 cm from the lower cut end.’
      • ‘Since most grooming occurs at night, high power halogen lights provide ample vision both front and rear while heated outside rear view mirrors allow for constant visibility.’
      • ‘Both Ceuta and Melilla are now surrounded by 10-foot fences studded with guard towers and movement sensors, topped with barbed wire and halogen searchlights.’
      • ‘In this treatment, the patient is secured to a dentist chair with leather straps and an extremely hot halogen lamp is left inches from their face for hours at a time.’
      • ‘The light source was a halogen lamp and light intensity was varied with neutral density filters.’


Mid 19th century: from Greek hals, halo- ‘salt’ + -gen.