What is a therasaus for?

It seems you're asking about a "therasaus," but there's no word like that in the English language. It's likely a misspelling of "thesaurus."

A thesaurus is a book or online resource that provides synonyms (words with similar meanings) and sometimes antonyms (words with opposite meanings) for a given word.

Here's how a thesaurus can be useful:

* Enriching your vocabulary: It can help you find more precise or interesting words to use in your writing or speaking.

* Avoiding repetition: If you're using the same word too often, a thesaurus can suggest alternatives.

* Improving your understanding of words: Exploring synonyms and antonyms can deepen your comprehension of a word's nuances.

If you were asking about something else, please clarify your question!