The article considers the nominative-derivational potential of the words polden and polnoch in the East Slavic languages. The nominative-derivational potential is understood as the ability of lexical units to produce nominative means. The objectives of the study include identifying the composition of the indicated vocabulary and the range of concepts they express for Old Rus and modern times. The analysis has involved about 200 units of nomination and showed that the East Slavic languages significantly developed these word families, with their nominative-derivational capabilities mainly realized in folk speech through rich lexical synonymy. The comparison has revealed a greater power of the word family polden compared to polnoch, as well as a greater formal-semantic variety of its derivatives, which is explained by its numerous meanings due to the special role of daylight in human life. The semantics of the source words determined the nature of the nominative spheres marked with derivative units (“Time”, “Nature”, “Man”), reflecting the accumulated socio-worldview experience of closely related peoples, their close relationship. The structure and meaning of derivatives in different languages have both common and special features. The commonnes is expressed by the unimodel formations and their synonymy (Rus. opolnoch, Ukr. opivnich, Bls. aponachy, Rusin. opivnich, upunochi), specificity – by their formal and meaningful uniqueness: Rus. mezhpolden ‘south side’, odnopoldenok ‘light time of day’, poldenoshnik‘milking bucket’, Ukr. adverbs pivdennishe, pivnichniche, Blr. names of mythological creatures, Rusin. dopoludnyar, ‘shepherdʼ, upidpoludne ʽ in the first half of the day’ and others. Together, they demonstrate the nominative-derivational potential of the names of the light and dark day time climax, which developed, inter alia, under the mutual influence of closely related languages.