hal ‧ o ‧ gen /ˈhælədʒ ə n/ BrE AmE noun [uncountable]
[ Date: 1800-1900 ; Language: Swedish ; Origin: Greek hals 'salt' ]
1 . a halogen light uses halogen gas to produce light
halogen bulb/lamp/light etc
2 . one of a group of five simple chemical substances that make ↑ compound s easily