Here's a breakdown:
* Dictionary: Provides definitions, pronunciations, and sometimes etymological information about words. It tells you what a word *means*.
* Thesaurus: Lists synonyms (words with similar meanings) and sometimes antonyms (words with opposite meanings) for a given word. It helps you find words that are *similar* in meaning but may be more precise, descriptive, or appropriate for your context.
Here are some situations where you might use a thesaurus:
* To avoid repetition: If you've used the same word several times in a sentence or paragraph, a thesaurus can help you find a more varied and interesting way to express yourself.
* To find a more precise word: Sometimes a thesaurus can help you find a word that expresses a particular nuance of meaning more accurately.
* To find a more formal or informal word: Depending on the context, you might need to find a more formal or informal synonym for a word.
However, keep these points in mind:
* Don't just blindly swap words: Always make sure that the synonym you choose fits the context and meaning of the original word. A thesaurus can be a helpful tool, but it shouldn't be used to simply replace words without understanding the nuances of meaning.
* Consider your audience: The level of formality and the type of language you use should be appropriate for your audience.
Ultimately, both dictionaries and thesauruses are valuable resources for writers and readers. Choose the one that best suits your needs for a particular task.