This article examines the issue of Arabic roots and stems in Old Uzbek from a comparative-historical and etymological perspective. The study focuses on the specific features of the Arabic triliteral root system, its historical development, and its connection with older biliteral Proto-Semitic roots. Based on the theoretical frameworks proposed by B. M. Grande and A. Jeffery, the article analyzes root homonymy, semantic expansion, and the differentiation of meanings in Arabic loanwords adopted into Old Uzbek. It is argued that Arabic borrowings entered Old Uzbek not at the level of abstract roots, but through historically formed and semantically stabilized nominal and verbal stems. Using examples such as kinship terms, as well as lexemes like sultan, salita, and madaniyat, the research reveals the multilayered etymological nature of Arabic loanwords. The findings demonstrate that Arabic exerted not only lexical but also profound historical and morphological influence on the formation of the Old Uzbek lexicon.