The principles of simplification/complication of definitions are analysed. It is proved structure of definitions without the generic terms available to children of preschool age. The principles of creation of the explanatory dictionary for children with different extent of cognitive development are proved.
The methods of definition construction are classified according to the information contained in them about relation of defined concept toward to the extension of contiguous concepts. The concepts are evaluated based on their informativeness and the number of words in them. Expediency of using different definitions is analysed for different aims. Drawn conclusion about expedience of the use of features of different definitions in planning of dictionaries constrution.
Ways to avoid circular definitions in the dictionaries are searched. Such decision is offered. For a parts of words which are names of simple features, should be formulated by means of definitions visual or operating meanings. By these words it is necessary to formulate definitions of complex features. By means of names of simple and complex features it is necessary to formulate abstract meanings of object names by means of a definitions.
Terms of neurology as a separate branch of medicine are considered in the article. Some features of their system organization are distinguished.