halogen

Concise Oxford English Dictionary © 2008 Oxford University Press:
halogen /ˈhalədʒ(ə)n, ˈheɪl-/

▶noun

• 1 Chemistry any of the group of reactive non-metallic elements fluorine, chlorine, bromine, iodine, and astatine.

• 2 [as modifier] denoting lamps and radiant heat sources using a filament surrounded by halogen vapour.

– derivatives
halogenic adjective.

– origin C19: from Gk hals, halo- ‘salt’ + -gen.