To have well developed lexical competence with a wide vocabulary is essential, not only for successful communication but also due to its impact on general knowledge, pupils' school success and their motivation to learn. Since not all pupils receive the same level of encouragement at home, the role of the school in building their vocabulary is crucial. One of the ways to build on lexical competence in class is to use a dictionary intended for pupils and adapted to their cognitive and linguistic abilities. This doctoral thesis focuses on the dictionary intended for primary school pupils aged 6-10, the so-called primary school dictionary. I will seek to define it and specify its characteristics and roles. Having reviewed foreign and Slovene reference works, analysed some foreign and Slovene school dictionaries, carried out a survey among teachers and pupils aged 8 and 11, examined pupils' essays and reviewed the Slovene syllabus and school materials for Slovene for pupils aged 6-12, I have established the existence of a need for a primary school dictionary. I, therefore, wish to define in as much detail as possible several issues related to the composition of such a reference book. This thesis will be a contribution to meta-lexicography and language didactics. Its topic, primary school dictionary, has not been explored in detail by many authors in Slovene scientific writings. I see it as a language didactics tool that aids pupils in developing their linguistic, and particularly lexical, competence. The thesis is also important for its applicative role: the proposed dictionary concept can serve as the basis for an actual primary school dictionary, the use of which should be encouraged by teachers of pupils aged 6-10 regardless of the subject being taught. And not least, this doctoral thesis should serve to facilitate the emergence of secondary school and upper secondary school dictionaries.