Which term best describes the belief in one God in Islam?

The belief in one God in Islam is best described by the term "monotheism." Monotheism is the theological position that asserts the existence of only one God and is a foundational concept in Islam. This belief emphasizes the oneness and singularity of God, which is central to the Islamic faith, as reflected in the core declaration of faith known as the Shahada.

While the Shahada is indeed significant in Islam as it is the testimony that "There is no god but Allah, and Muhammad is His messenger," it is a declaration of faith rather than a term that encompasses the entire concept of the belief in one God.

Sewah and Hadith are not relevant to the definition of monotheism; Sewah seems to be a misinterpretation or misspelling of a term unrelated to Islamic theology, while Hadith refers to the recorded sayings and actions of the Prophet Muhammad, providing guidance for Muslims but not specifically addressing the nature of God.

Thus, monotheism accurately encapsulates the essence of the belief in one God that is central not just to Islam, but to several other major world religions as well.