This graduate thesis is focused on synonymy as lingual universality and frequency of synonymy in Croatian language textbooks for the first grade of primary school. Synonymy is most often defined as semantic relationship between two or more lexemes that belong to the same type of word and have different expressions but their contents partially or completely match. During education students will, in Croatian language classes but also in textbooks and book report classes, encounter synonymy and different types of synonyms and lexical exercises with synonyms, which always must be adapted to the age and language development of the individual, and they are present from the beginning of primary education. It is extremely important that the teacher gives students, from the very beginning of primary education, the opportunity to realize that there are lexemes that have different expressions and whose contents partially or completely match. The analysis of textbook sets for the Croatian language for the first grade of primary school singled out synonymous pairs/series that appear in the analyzed material, also for each synonymous pair/series it is determined which type of synonymy is it and for each synonymous pair/series is listed an example which appears in the corpus. Based on the tabulated results it can be seen that the appearance of synonymy is justified, ie that synonymy as a lingual universality by its appearance in textbooks can be stimulating for the language development of younger school age students.