Dictionaries are used as reference materials and are compiled by linguists who are lexicographers. There is an extensive lexicon of English language and does vary with respect to professions as well. A comprehensive set of principles are used by lexicographers to compile words with respect to their usage and connotation in language. There is variation in spoken and written language as well which is indicated in any good dictionary. Besides that, words are listed along with the part of speech they relate to, their usage with examples and their pronunciation using phonetic signs.