The article presents results of a contrastive-comparative study of the definitive substantive compound and the word combination with relative adjective depending on the use case. The reason why they can be compared is that, in modern German, both the first component of the compound noun and the relative adjective express the object-relative meaning. The study material is taken from the German Reference Corpus (Deutsches Referenzkorpus, DeReKo) of written texts of the Institute of German Language in Mannheim. This paper considered attributive constructions with the determining components pflanzlich - Pflanzen-, tierisch - Tier-, ärztlich - Arzt-/Ärzte-, studentisch - Student-, using the method of field structuring that was developed and introduced into the lexical-grammatical studies by V. G. Admoni. The method takes into account the multidimensionality, heterogeneity and continuity of lexical-grammatical phenomena, identifying the central area of manifestation of a specified feature and the periphery zone. The choice between an attributive construction and a compound noun depends on the lexical meaning of determining and determinate components, the lexicalization stage, and the influence of context. Although the functional boundaries of every compared pair are individual, both attributes share a specific area of usage. In some cases, preference for one of the attributes is owed to traditions of specific functional styles; in other cases, usage frequencies differ only slightly. For some attributive constructions and compound nouns, specific usage areas could be identified. The research contributes to the study of functional-semantical features of synonymic lexical-grammatical language phenomena, identifies their differential features and sets the boundaries of their shared usage area.