halogen

n. any of a number of electronegative elements which form a salt when united with metals (Chemistry)

The halogens or halogen elements are a series of nonmetal elements from Group 17 (old-style: VII or VIIA; Group 7 IUPAC Style) of the periodic table, comprising fluorine, F; chlorine, Cl; bromine, Br; iodine, I; and astatine, At. The undiscovered element 117, temporarily named ununseptium, may also be considered a halogen.
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Noun
1. any of five related nonmetallic elements (fluorine or chlorine or bromine or iodine or astatine) that are all monovalent and readily form negative ions
(hypernym) group, grouping
(hyponym) astatine, At, atomic number 85

n. halogen, any of a number of electronegative elements which form a salt when united with metals (Chemistry)

adj. halogenous, of or pertaining to halogen

(n.)
An electro-negative element or radical, which, by combination with a metal, forms a haloid salt; especially, chlorine, bromine, and iodine; sometimes, also, fluorine and cyanogen. See Chlorine family, under Chlorine.