Dictionaries are books which are used to research the definition of words. The dictionary will also give the part of speech of the particular word being researched. Some dictionaries also provide legends of different signs and symbols such as in Astronomy, Chemistry, Medicine and Pharmacy. Thesauruses are books which will list words which are grouped together according to similarity of meaning. Synonyms and sometimes antonyms are provided as well. Roget's Thesaurus was published reportedly in 1852 and was compiled by Peter Mark Roget. The book was based on concepts it is said rather than in alphabetical order.
