In recent years, Turkey has seen an increase in lexicological studies, particularly those focused on methodology. One of the fields of study on methodology is the problem of how to define the headings in a monolingual dictionary. Since definition is an endeavour to understand the truth of things, it is an issue that concerns many disciplines. A dictionary, by collecting words from various fields under its covers, serves as a reference for those working in diverse domains. Therefore, it’s fair to state that the definition of dictionary headings requires substantial effort during the dictionary’s assembly. While the issue of definition concerns multiple scientific branches, the question of what constitutes a suitable definition falls within the purview of both classical logic and lexicography. It is seen that these principles overlap with each other at many points. In this study, the “principles of definition” found in the works on logic and on lexicography are analysed separately and examples from the Turkish Dictionary were added for each principle. Afterwards, a single list was tried to be formed by combining the principles existing in the two fields. These principles were analysed comparatively with examples from TDK Türkçe Sözlük, Misalli Büyük Türkçe Sözlük and Ötüken Türkçe Sözlük, which are reference sources for contemporary Turkish. The principles were then explained through definitions.

Definition, lexicography, classical logic, Turkish.