The dictionaries, which are compiled for a special purpose or aspects of a language, are called special dictionaries. Most of these aspects of words, which are separately dealt with in special dictionaries; are also covered in general dictionaries. Hence, they are sometimes known as supplementary wordbooks. They deal with the special aspects of the words much more comprehensively than the general dictionaries. There are numerous forms and varieties of specialised dictionaries. Here, they are divided into three groups according to their content and scope.