What Reference books that contain words of similar meanings and opposite are called?

The reference books that contain words of similar meanings (synonyms) and opposite meanings (antonyms) are called thesauruses.

Here's a breakdown:

* Synonym: A word that has the same or nearly the same meaning as another word.

* Antonym: A word that has the opposite meaning of another word.

* Thesaurus: A dictionary of synonyms and antonyms.

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