What is the meaning of the word "Āmīn"?

Imam Ibn al-Jawzī (d. 597/1201) summarized the scholars' opinions in his book "Zād al-Masīr" as follows:

1. "So let it be" (as requested). [Attributed by Ibn al-Anbārī to Ibn ʿAbbās and al-Ḥasan]
2. "O Allah, answer (our supplication)". [Al-Ḥasan, al-Zajjāj]
3. That it is one of Allah's names. [Mujāhid,Hilāl ibn Yasāf, Jaʿfar ibn Muḥammad]