This paper offers a contrastive-functional analysis of the Arabic case forms jarr and naṣb in Modern Standard Arabic and compares their functional distribution with the agglutinative case system of modern standard Azerbaijani. We argue that the traditional identification of jarr with the genitive case and naṣb with the accusative case fails to capture the actual range of grammatical functions encoded by these forms. On the basis of empirical data from Modern Standard Arabic, we demonstrate that jarr functions as a polyfunctional case domain encompassing at least four major subdomains: possession and attributive relations in iḍāfa constructions, direction of motion, location, and source of motion. The form naṣb, in turn, covers a cluster of distinct functions, including direct object marking, adverbial meanings of time, manner, and degree (notably in ḥāl and maf`ūl muṭlaq constructions), as well as modal, focal, and emphatic roles. The contrastive comparison with Azerbaijani shows that these functional subdomains correspond to several formally independent case categories and syntactic devices, revealing a systematic asymmetry in form-function mapping. While Arabic exhibits a many-to-one mapping between morphological form and grammatical function, Azerbaijani displays a predominantly one-to-one mapping. We conclude that jarr and naṣb should be analyzed not as specialized case markers, but as polyfunctional case domains. This perspective contributes to contrastive Arabic-Turkic grammar and to a broader typological understanding of case systems.