noun

thesaurus

thih-SAW-ruhs

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Thesaurus (noun) means a reference book or website that groups words by meaning, so you can look up a word and find its synonyms and often its antonyms. Example: “I keep a thesaurus open when I'm editing to avoid repeating myself.”

noun

A reference book or website that groups words by meaning, so you can look up a word and find its synonyms and often its antonyms.

"I keep a thesaurus open when I'm editing to avoid repeating myself."

"Don't just grab the longest word the thesaurus offers."

A controlled list of indexing terms and their relationships, used to catalogue and search a collection of documents.

"Articles are tagged using the library's medical subject thesaurus."

How to use thesaurus

Learner’s notes

In plain EnglishA book or site that gives you other words meaning roughly the same thing.

When to use it

Neutral. The plural is thesauruses in ordinary use and thesauri in more formal or academic writing; both are accepted.

Memory tip

A thesaurus tells you what else you could say; a dictionary tells you what a word actually means. Always check an unfamiliar synonym in a dictionary before using it.

Trace the full origin ↓

Easily confused with

dictionary → glossary → lexicon →

Common pairings

look it up in a thesaurus thesaurus entry online thesaurus

Vocabulary Flow

Build your vocabulary from words like thesaurus.

Vocabulary Flow serves the next word, and the next — meaning, pronunciation and an example each time. Practice at your level, or learn English in your own language.

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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 “thesaurus” A quick quiz — meaning, synonyms & usage →

Fill the gap

Can you complete this real example?

I keep a _____ open when I'm editing to avoid repeating myself.

Etymology

From Latin thesaurus 'treasure, treasury, storehouse', from Greek thesauros.

Origin: Latin

Synonyms

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synonym dictionary wordbook controlled vocabulary taxonomy

Related words

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Rhymes for thesaurus

Taurus tyrannosaurus

See all rhymes for thesaurus →

Frequently asked questions

What is the difference between a thesaurus and a dictionary?

A dictionary is organised by headword and tells you what each word means, how it is pronounced and where it came from. A thesaurus is organised by meaning and gives you alternative words that express a similar idea. Writers use both together — the thesaurus to find a candidate, the dictionary to check it fits.

What is the plural of thesaurus?

Both thesauruses and thesauri are correct. Thesauruses is more common in everyday English; thesauri keeps the Latin plural and appears more in academic and library contexts.

Why is it called a thesaurus?

The word is Latin for treasury or storehouse, itself from Greek. The idea is a store of words you can draw on, and the sense of a hoard of treasure is the older meaning of the Latin term.

What is the meaning of thesaurus?

"thesaurus" (noun) means a reference book or website that groups words by meaning, so you can look up a word and find its synonyms and often its antonyms.

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