The word "thesaurus" comes from the Greek θησαυρός, which means "treasure." In linguistics, a thesaurus is a special kind of dictionaries that contain information about the semantic relationships of lexical units. In information theory, a thesaurus is a set of information available to a subject.
In a broad sense, a thesaurus denotes a system of knowledge, which is possessed by any subject or group of subjects, about reality. The subject is also able to receive new information, due to which the original thesaurus will change. The thesaurus contains not only information about reality, but also additional information, due to which it becomes possible to receive new information. In the 1970s, information retrieval thesauri became widespread. They include a lexical unit called a descriptor. It serves to search for information in automatic mode. Each word of the thesaurus is associated with a synonymous descriptor for which semantic relations are set. Hierarchical (genus-specific) relations and associative ones are distinguished. In linguistics, semantic relations that are included in the thesaurus can be antonyms, hyponyms, synonyms, paronyms, etc. Thesauri, expressed in electronic format, can be effective tools with which you can describe specific subject areas. If an explanatory dictionary is aimed at revealing the meaning of a word solely by means of definition, then a thesaurus helps to reveal it by using the relationship of a word with other words and their groups. This allows you to use the thesaurus to work with AI-powered knowledgebase populations. In Microsoft Word, there is a tool called the Thesaurus. With its help, you can view synonyms for any word, or search for its definitions. This allows you to expand your vocabulary, learn synonyms for already known words. To use this tool, you need to select the desired word in the document, then right-click on it, select "Synonyms", and then "Thesaurus".