A thesaurus is a reference book or online resource that lists synonyms (words with the same or similar meaning) and sometimes antonyms (words with opposite meanings) for a given word.
There are many popular online thesauruses, like:
* Merriam-Webster Thesaurus: [https://www.merriam-webster.com/thesaurus](https://www.merriam-webster.com/thesaurus)
* Dictionary.com Thesaurus: [https://www.dictionary.com/browse/thesaurus](https://www.dictionary.com/browse/thesaurus)
* Oxford Thesaurus: [https://www.oxfordlearnersdictionaries.com/](https://www.oxfordlearnersdictionaries.com/)
These are just a few examples. There are many other options available.