Īlthough the first recorded dictionaries date back to Sumerian times (these were bilingual dictionaries), the systematic study of dictionaries as objects of scientific interest themselves is a 20th-century enterprise, called lexicography, and largely initiated by Ladislav Zgusta. "informal" or "vulgar") in many modern dictionaries are also considered by some to be less than objectively descriptive. There is also a contrast between prescriptive or descriptive dictionaries the former reflect what is seen as correct use of the language while the latter reflect recorded actual use. The word dictionary (unqualified) is usually understood to refer to a general purpose monolingual dictionary. There are other types of dictionaries that do not fit neatly into the above distinction, for instance bilingual (translation) dictionaries, dictionaries of synonyms ( thesauri), and rhyming dictionaries. In practice, the two approaches are used for both types. In theory, general dictionaries are supposed to be semasiological, mapping word to definition, while specialized dictionaries are supposed to be onomasiological, first identifying concepts and then establishing the terms used to designate them. Lexical items that describe concepts in specific fields are usually called terms instead of words, although there is no consensus whether lexicology and terminology are two different fields of study. Specialized dictionaries include words in specialist fields, rather than a complete range of words in the language. Ī broad distinction is made between general and specialized dictionaries. It is a lexicographical reference that shows inter-relationships among the data. A dictionary is a listing of lexemes from the lexicon of one or more specific languages, often arranged alphabetically (or by radical and stroke for ideographic languages), which may include information on definitions, usage, etymologies, pronunciations, translation, etc.