chlorine

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A highly irritating, greenish-yellow halogen element, existing as a diatomic gas, Cl₂, and capable of combining with nearly all other elements, produced principally by electrolysis of sodium chloride and used widely to purify water, as a disinfectant and bleaching agent, and in the manufacture of many important compounds including chlorates, sodium hypochlorite, and chloroform. Atomic number 17; atomic weight 35.453; freezing point −100.5°C; boiling point −34.04°C; specific gravity 1.56 (−33.6°C); valence 1, 3, 5, 7. cross-reference: Periodic Table.

from The Century Dictionary.

• noun See chlorin.
• Of the color of young leaves; light green.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Chem.) One of the elementary substances, commonly isolated as a greenish yellow gas, two and one half times as heavy as air, of an intensely disagreeable suffocating odor, and exceedingly poisonous. It is abundant in nature, the most important compound being common salt (Sodium chloride). It is powerful oxidizing, bleaching, and disinfecting agent. Symbol Cl. Atomic weight, 35.4.
• noun the elements fluorine, chlorine, bromine, and iodine, called the halogens, and classed together from their common peculiarities.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A toxic, green, gaseous chemical element (symbol Cl) with an atomic number of 17.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a common nonmetallic element belonging to the halogens; best known as a heavy yellow irritating toxic gas; used to purify water and as a bleaching agent and disinfectant; occurs naturally only as a salt (as in sea water)