Dictionaries dealing with the terms of a particular subject are known as subject dictionaries. The rapid development in all the fields of knowledge, has necessitated in the compilation of subject dictionaries devoted to the specific subject fields, occupations and professions. This is especially true for the fast advancing subjects of science and technology. Common dictionaries cover many terms of the subjects in humanities. As specialisation raises, so do the scientific dictionaries. They differ from general language dictionaries in two ways:
They include specialised technical terms of a particular discipline not usually found in general dictionaries. These technical terms are invented, borrowed, adopted, adapted and invented by specialists and experts in the fields.
They give detailed descriptions of words. They not only define the terms but explain and comment on them. Some subject dictionaries are meant for general public whereas most of them are published for subject specialists and students. They are found in various forms according to the size, volume and language. They can be