hal·o·gen 
(hălə-jən)
(hălə-jən)n.
Any of a group of five chemically related nonmetallic elements including fluorine, chlorine, bromine, iodine, and astatine.
adj.
1. Of or relating to the group of elements that are halogens.
2. Of or relating to a bright incandescent light bulb containing a halogen gas that prevents the filament from disintegrating at higher temperatures.
[Swedish : halo-, halo- + -gen, -gen.]
ha·loge·nous (hă-lŏjə-nəs) adj.