A book or an electronic resource to which one can refer for information and authoritative facts. Reference works are usually referred to for particular pieces of information, and the information is compiled for ease of reference, e.g. by using indices. Examples include encyclopaedias, dictionaries, manuals, lexica, thesauri, catalogues, bibliographies, atlases, glossaries, handbooks.

(plural thesauri or thesauruses). A reference work for finding synonyms of words. Words are usually either grouped in a hierarchicaly taxonomy of concepts or organized alphabetically. Some thesauri additionally provide information on the distinctions between similar words, often by describing their meanings and usages or their connotations.