THESAURUS,  A TYPE OF DICTIONARY
A thesaurus is a dictionary that helps you find synonyms or near-synonyms (words that have the same or almost the same meaning as the word you have in mind but do not want to use). Using a thesaurus when writing can make your writing more varied and precise. Many native writers find the thesaurus an invaluable tool.

All the web thesauri are fast to use, but knowing whether the synonym can be used in the intended context is more difficult. The Collins COBUILD concordancer may help you when deciding whether a certain word can be used in your sentence. Click tasks to try an exercise on thesaurus use.

THESAURI
Merriam-Webster's thesaurus is one of the well-known thesauri.
The Wordsmyth site may be able to help you.
Why not try Roget's Thesaurus - another well-known thesaurus.