chlorine

American  

[klawr-een, -in, klohr-] / ˈklɔr in, -ɪn, ˈkloʊr- /

noun

chlorines plural

1. a halogen element, a heavy, greenish-yellow, incombustible, water-soluble, poisonous gas that is highly irritating to the respiratory organs, obtained chiefly by electrolysis of sodium chloride brine: used for water purification, in the making of bleaching powder, and in the manufacture both of chemicals that do not contain chlorine, as ethylene glycol, and of those that do. Cl; 35.453; 17.

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chlorine British  

/ ˈklɔːriːn, ˈklɔːrɪn /

noun

1. a toxic pungent greenish-yellow gas of the halogen group; the 15th most abundant element in the earth's crust, occurring only in the combined state, mainly in common salt: used in the manufacture of many organic chemicals, in water purification, and as a disinfectant and bleaching agent. Symbol: Cl; atomic no: 17; atomic wt: 35.4527; valency: 1, 3, 5, or 7; density: 3.214 kg/m³; relative density: 1.56; melting pt: –101.03°C; boiling pt: –33.9°C

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chlorine Scientific  

/ klôr′ēn′ /

1. A greenish-yellow, gaseous element of the halogen group that can combine with most other elements and is found chiefly in combination with the alkali metals as chlorates and chlorides. Chlorine is highly irritating and poisonous. It is used in purifying water, as a disinfectant and bleach, and in the manufacture of numerous chemical compounds. Atomic number 17; atomic weight 35.453; freezing point −100.98°C; boiling point −34.6°C; specific gravity 1.56 (−33.6°C); valence 1, 3, 5, 7.

2. See Periodic Table See Note at chlorophyll

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chlorine Cultural  

1. A chemical element, normally a corrosive gas, that is widely used for sterilization and cleaning.

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Discover More

Chlorine in CFCs is believed to be responsible for the ozone hole.

Chlorine is added to drinking water to kill bacteria.

Other Word Forms

Derived Forms

• chlorinous
  adjective

Inflected Forms

Nouns

• chlorines
  plural

Etymology

Origin of chlorine

First recorded in 1800–10; chlor- ¹ + -ine ²

Compare meaning

How does chlorine compare to similar and commonly confused words? Explore the most common comparisons:

• chlorine vs. chloride
• chloramine vs. chlorine

Explanation

Chlorine is a chemical that's commonly used to purify water. That bleach-like smell at the public swimming pool? That's chlorine. At room temperature, chlorine is a greenish-yellow gas. It was identified as a separate element in 1810 by the British chemist Sir Humphry Davy, who named it after the Greek khlōros, "pale green." Modern uses of chlorine have ranged from a weapon in chemical warfare to public sanitation. Today, most public water is treated with chlorine to kill dangerous bacteria.

Example Sentences

The National Park Service said it is using pumps to treat the water with what it called nanobubble ozone technology to kill the algae, along with hydrogen peroxide, which it said is milder than chlorine.

From Barron's • Jun. 16, 2026

Some rocket fuel also directly adds chlorine to the atmosphere.

From The Wall Street Journal • Jun. 11, 2026

And in 1989, thousands had to flee when poisonous chlorine gas leaked from a 30-ton tank in Ventura County, injuring about 20 people.

From Los Angeles Times • Jun. 6, 2026

The group have packed filter systems and chlorine pills to treat any water they take from streams.

From BBC • May 20, 2026

Even the elevator smells of chlorine and has a wet floor.

From "The Miscalculations of Lightning Girl" by Stacy McAnulty

Related Words

• bleach
• disinfectant