A thesaurus is a formal arrangement of terms in a way that reveals their logical and semantic relationships. The most common descriptors are USE, UF (use for), BT (broader term), NT (narrower term) and RT (related term). It can be used by humans to determine an appopriate term to use in a given context or by software to broader or narrow a search based on a given query term.

• Art and Architecture Thesaurus (AAT) - provides vocabulary for topic, form and genre, occupation, function, the materials of which items are made, and the processes and techniques of their making
• Australian Public Affairs Information Service (APAIS) Thesaurus - controlled vocabulary of subject terms used to index articles for APAIS
• Bioethics Thesaurus - controlled vocabulary developed at the Kennedy Institute of Ethics, Georgetown University, specifically for the cross-disciplinary field of bioethics
• Center For Army Lessons Learned (CALL) Dictionary and Thesaurus
• Functional Thesauri
• AGIFT (Australian Government's Interactive Thesaurus) - (requires Microsoft Excel 97 or Excel 97 Viewer)
• Functional Index - National Archives of Australia
• Keyword AAA - National Archives of Australia
• A Thesaurus of General Terms for the Commonwealth: Assessment of Keyword AAA - National Archives of Australia
• Understanding official government terminology: Natural language searching and Government thesauri - National Archives of Australia
• High-Level Thesaurus (HILT) Project - aims to research, report, and make recommendations on the problems of cross-searching and browsing by subject across a range of communities, services, and service or resource types, includes lists of Additional Sources
• MultiTes: Thesaurus Construction Made Easy
• National Aeronautics and Space Administration (NASA) Thesaurus
• Roget's Thesaurus
• Seattle City Clerk Thesaurus
• Specification and standardization of data elements (ISO 11179)
• Thesauri Online
• Thesaurus for Graphic Matierals (TGM) - two parts: Subject Terms (TGM1) is a source for topical terms for graphic materials, based on LCSH; Genre and Physical Characteristic Terms (TGM2) provides terminology for the description of the form and genre of these types of materials
• Thesaurus of Educational Resource Information Center (ERIC) Descriptors
• Thesaurus of Geographic Names (TGN) - hierarchically structured listing of geographic names worldwide, including historical names, linked to their modern equivalents
• United Nations Educational, Scientific and Cultural Organization (UNESCO) Thesaurus
• Web Thesaurus Compendium