In the field of information retrieval, a thesaurus is defined as a controlled and structured vocabulary in which concepts are represented by terms. Terms are organised so that relationships between concepts are made explicit. Preferred terms are accompanied by lead-in entries for synonyms or quasi-synonyms (see the relevant international standard). One example of a thesaurus that you might have come across is MeSH, the US National Library of Medicine’s thesaurus of Medical Subject Headings (Figure 10).
The NLM provides a series of webinars and tutorials about MeSH; one that may be of particular interest is Searching Drugs or Chemicals in PubMed. The primary advantage of a thesaurus compared with a non-hierarchical list is that, if the synonyms are well defined, the user can find information without using the exact terminology used by the person who created the database record.
Figure 10 A snapshot of the entry for protein tyrosine kinases in MeSH; synonyms are labelled as ‘Entry term’.