n. [ Gr. "a`ls, "alo`s, salt + -gen: cf. F. halogène. ] (Chem.) An electro-negative element or radical, which, by combination with a metal, forms a haloid salt; especially, chlorine, fluorine, bromine, and iodine; sometimes, also cyanogen. See Chlorine family, under Chlorine. [ 1913 Webster ]
(n) any of five related nonmetallic elements (fluorine or chlorine or bromine or iodine or astatine) that are all monovalent and readily form negative ions