Why is the word "Aqeedah" used, even though it was not mentioned in revelation and is not a religion, given the presence of the word "Millah" in the Qur'an, and Allah's word is above any terminology?

It suffices, in clarifying the legitimacy of the term "Aqeedah" (creed), to dispense with undue formality in terminology. It does not contradict the Sharia; rather, it encompasses the terms of revelation related to it, such as "Iman" (faith) and "Wahy" (revelation). Its linguistic root has appeared in Sharia texts, among them the saying of the Prophet, peace and blessings be upon him: "The heart of a Muslim does not hold firm to three characteristics except that he enters Paradise." Furthermore, it was used by the Companions, the Tabi'un, and scholars of the first three centuries in their writings, such as Abu Ubayd al-Qasim ibn Salam, Ibrahim ibn Khalid Abu Thawr, Imam Muhammad ibn Nasr al-Marwazi, and Imam al-Tahawi in "Al-Aqeedah al-Tahawiyah." Scholars have used this term without objection, which is sufficient to demonstrate its legitimacy.