Functions of a Thesaurus 

The major functions of a thesaurus include the following : 

a) it provides a standard vocabulary for a given subject field by exercising control on the vocabulary of terms used in an indexing language. Methods of controlling the vocabulary are: 

1. out of all possible synonyms and quasi-synonyms, only one term is selected as a descriptor, 
2. the scope of the meaning of the term is clearly indicated in a scope note for the best suitability of the selected meaning, 
3. a definite rule is followed for compound terms, word-forms, number (singular/plural) and spellings are standardized, and 
4. homonyms are differentiated by qualifiers;

b) it shows the intrinsic, semantic relationship existing between, terms, and thus provides system of references between terms; 

c) it helps the indexer and the searcher in the choice of preferred terms; 

d) it provides hierarchical display of terms so that a search can be broadened or narrowed systematically; 

e) it increases the speed of retrieval by use of indexing terms and search terms; and 

f) it provides a map of a 'given subject field, which helps to understand the structure of the field.