collection of the words of a language, dialect or subject, arranged
alphabetically or in some other definite order, and with explanations in
the same or some other language. When the words are few in number, being
only a small part of those belonging to the subject, or when they are
given without explanation, or some only are explained, or the
explanations are partial, the work is called a _vocabulary_; and when
there is merely a list of explanations of the technical words and
expressions in some particular subject, a _glossary_. An alphabetical
arrangement of the words of some book or author with references to the
places where they occur is called an index (q.v.). When under each word
the phrases containing it are added to the references, the work is
called a _concordance_. Sometimes, however, these names are given to
true dictionaries; thus the great Italian dictionary of the _Accademia
della Crusca_, in six volumes folio, is called _Vocabolario_, and
Ernesti's dictionary to Cicero is called _Index_. When the words are
arranged according to a definite system of classification under heads
and subdivisions, according to their nature or their meaning, the book
is usually called a classed vocabulary; but when sufficient explanations
are given it is often accepted as a dictionary, like the _Onomasticon_
of Julius Pollux, or the native dictionaries of Sanskrit, Manchu and
many other languages.

Dictionaries were originally books of reference explaining the words of
a language or of some part of it. As the names of things, as well as
those of persons and places, are words, and often require explanation
even more than other classes of words, they were necessarily included in
dictionaries, and often to a very great extent. In time, books were
devoted to them alone, and were limited to special subjects, and these
have so multiplied, that dictionaries of things now rival in number and
variety those of words or of languages, while they often far surpass
them in bulk. There are dictionaries of biography and history, real and
fictitious, general and special, relating to men of all countries,
characters and professions; the English _Dictionary of National
Biography_ (see BIOGRAPHY) is a great instance of one form of these;
dictionaries of bibliography, relating to all books, or to those of some
particular kind or country; dictionaries of geography (sometimes called
_gazetteers_) of the whole world, of particular countries, or of smal