What does a thesaurus provide?

A thesaurus primarily serves as a resource for finding synonyms, which are words that have similar meanings. It helps users discover alternative vocabulary options that can enhance writing by providing more precise or varied language. This is particularly useful for individuals looking to improve their expression in writing or speaking by avoiding repetition.

The other options revolve around different aspects of language reference. Grammatical rules are typically found in grammar guides, while definitions of words are provided by dictionaries. Examples of correct usage can be found in style guides or usage manuals. Thus, the primary function of a thesaurus is to offer suggestions for better synonyms, making the provided answer the most appropriate choice.