This paper examines the crucial theological and exegetical role of the Greek word μονογενής in the formulation and logic of the Nicene Creed, both in its original form from the Council of Nicaea (325) and its revised form from the Council of Constantinople (381). In the Creed of Nicaea (325), Christians are called to confess belief “in one Lord Jesus Christ, the Son of God, begotten of the Father as only-begotten, that is, of the essence of the Father.” Though the wording of the Nicene Creed (381) differs slightly, the term μονογενής remains central: “We believe … in one Lord Jesus Christ, the only-begotten Son of God, begotten of the Father before all worlds.” In both creeds, μονογενής functions as a linchpin, connecting the affirmation of the Son’s begottenness to the claim of his consubstantiality with the Father. While many modern interpreters have argued that μονογενής should be understood as meaning “unique” or “only Son” rather than “only begotten,” this paper contends that readings which remove or conceal the concept of “begotten” fail to account for the theological function of the term within the creed’s scriptural logic. In particular, I argue that the phrase “begotten, not made” is not an abstract metaphysical assertion, but a direct consequence of the meaning of μονογενής as it was understood in the fourth century, in light of its Johannine usage. To support this claim, the paper considers the use of μονογενής in key Johannine texts (John 1:14, 18), alongside patristic sources such as the letter of Alexander of Alexandria (324), which clearly links μονογενής with the Son’s eternal generation from the essence of the Father. This historical and theological context demonstrates that the Creed’s affirmation of the Son as “begotten, not made” is grounded in a reading of μονογενής that includes the idea of begottenness, not mere uniqueness. The paper concludes by urging modern translators and theologians to preserve this semantic and theological connection in their renderings of μονογενής, so that contemporary readers can perceive the deep coherence between Johannine Christology and Nicene orthodoxy.