The word thesaurus means 'treasury' or 'storehouse' in Greek and Latin is used to refer to several varieties of language resources, it is most commonly known as a book that groups words in synonym clusters and related meanings. Its original sense of 'dictionary or encyclopedia' has been overshadowed by the emergence of the Roget-style thesaurus and it is considered as a writing aid as it helps writers with the selection of words. The differences between a Roget-style thesaurus and a dictionary would be the indexing and information given; the words in thesaurus are grouped by meaning, usually without definitions, while the latter is by alphabetical order with definitions. When users are unable to find a word in a dictionary, it is usually due to the constraint of searching alphabetically by common and well-known headwords and the use of a thesaurus eliminates this issue by allowing users to search for a word through another word based on concept.