Merriam-Webster: Thesaurus

• Zthes: a Z39.50 Profile for Thesaurus Navigation
• Library of Congress Classification Schedules
• Getty Thesaurus of Geographic Names
• Art and Architecture Thesaurus
• Thesaurus of Musical Instruments
• The Astronomy Thesaurus
• Library of Congress Thesauri
• Babynames Thesaurus
• Inter Active Terminology for Europe (IATE)
• Phrases Thesaurus
• Power Thesaurus
• Beautiful Synonyms