The Penguin Thesaurus
With nearly 400,000 synonyms and antonyms, the Penguin Thesaurus is the most extensive, authoritative and modern wordfinder currently available.
Its alphabetical arrangement of the headwords means that it is very easy to use. In addition where a headword has more than one meaning or nuance there are examples to help the reader locate which group of synonyms are appropriate.
The coverage is the most up-to-date (including many slang and informal usages) of any thesaurus available.