A thesaurus helps you find the right word when the first one that comes to mind is too casual, too vague, or already used three times on the page. It makes your writing more varied and more precise.
A rich vocabulary is one of the things that make a good writer. Yet sometimes it is simply impossible to remember many different words for the same action, condition, or thing. This is where a thesaurus comes in handy.
What is a thesaurus?
A thesaurus is a reference work that lists words grouped by their meaning. Besides synonyms (words with a similar meaning), many also list antonyms (words with the opposite meaning). Even though a thesaurus lists many words with a shared meaning, do not expect any list to be complete.
The name fits. According to the Online Etymology Dictionary, thesaurus comes from the Latin thesaurus, from the Greek thesauros: "a treasure, a treasury, a storehouse". A thesaurus is a treasury of words.
Benefits
The benefits of such a collection of words with related meanings are obvious.
When you write a scientific paper, an essay for school or university, or an official letter or statement, some words sound out of place and too casual for the purpose. A thesaurus helps you find a more fitting one, so that your writing sounds more professional and competent.
When you write short stories, novels, or other fiction that is meant to be read by more than just the author, repeating the same words over and over becomes a nuisance for the reader. Using different words with the same or a slightly different meaning brings variety into the text, keeps the reader interested, and adds nuance and depth to your writing. 50 synonyms for "talking" shows how much choice a single verb can offer.
Synonyms are rarely exact, though. If a word in the list is new to you, look it up in a dictionary before you use it, so that it means what you want it to mean.
How to use a thesaurus
There are different ways to use a thesaurus.
Most word processors have one built in. In Microsoft Word, you find it on the Review tab, or you can right-click a word and choose Synonyms. In LibreOffice Writer, it is under Tools.
There are also online thesauruses, for example Thesaurus.com or the thesaurus of the Collins Dictionary.
Once you have replaced the words you repeated, check the finished text. The Spell Checker marks spelling and grammar mistakes, and its Picky mode also points out repetition and wordy phrases.