noun

caesium

SEE-zee-um

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Caesium (noun) means a soft, golden, highly reactive metallic element with the symbol Cs and atomic number 55. Example: “Caesium belongs to the alkali metals, alongside sodium and potassium.”

noun

A soft, golden, highly reactive metallic element with the symbol Cs and atomic number 55.

"Caesium belongs to the alkali metals, alongside sodium and potassium."

"The chemistry teacher explained that caesium is far too reactive to be left exposed to the air."

"On the periodic table, caesium is shown with the symbol Cs."

How to use caesium

Learner’s notes

In plain EnglishCaesium is a soft, golden, very reactive metal with the symbol Cs.

When to use it

Caesium is a technical, scientific word, and British writing normally uses this spelling.

Memory tip

Stress the first syllable: SEE-zee-um. British English keeps the ae spelling, and American English writes it cesium.

Trace the full origin ↓

Easily confused with

calcium →

Common pairings

caesium atom caesium metal caesium chloride caesium compound

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C2 · Advanced serendipity Fortunate discoveries made entirely by accident.

Gen Z slang rizz Charm — the ability to attract a romantic interest.

B2 · Intermediate empathy The capacity to share another person’s feelings.

C1 · Advanced nonchalant Casually calm and relaxed; unconcerned.

Internet slang delulu Delusional — believing something against the odds.

Etymology nostalgia Greek nostos “return home” + algos “pain”.

C2 · Advanced serendipity Fortunate discoveries made entirely by accident.

Gen Z slang rizz Charm — the ability to attract a romantic interest.

B2 · Intermediate empathy The capacity to share another person’s feelings.

C1 · Advanced nonchalant Casually calm and relaxed; unconcerned.

Internet slang delulu Delusional — believing something against the odds.

Etymology nostalgia Greek nostos “return home” + algos “pain”.

Test yourself on “caesium” A quick quiz — meaning, synonyms & usage →

Fill the gap

Can you complete this real example?

_____ belongs to the alkali metals, alongside sodium and potassium.

Etymology

The word was formed in Latin-based scientific vocabulary from caesius, meaning sky-blue, with the suffix -ium used for chemical elements. The blue reference relates to the element's radiation spectra.

Origin: Latin

Rhymes for caesium

curium osmium cerium erbium sodium helium barium radium cadmium fermium gallium niobium

See all rhymes for caesium →

Frequently asked questions

What is caesium?

Caesium is a chemical element with the symbol Cs and atomic number 55. It is a soft, golden, highly reactive alkali metal.

Is caesium the same as cesium?

Yes. Cesium is the American spelling of the same element, while caesium is the spelling used in British English.

Why is caesium called caesium?

The name comes from the Latin word caesius, meaning sky-blue, in reference to the element's radiation spectra. The ending -ium is the usual suffix for element names.

What is the meaning of caesium?

"caesium" (noun) means a soft, golden, highly reactive metallic element with the symbol Cs and atomic number 55.