Hebrew. An expression of assent said at the conclusion of prayers, very much as in our Christian worship. It is always used at the conclusion of the Suratu ‘l-Fatihah, or first chapter of the Qur’an.
Amin,”Faithful.” Al-Amin is the title which it is said was given to Muhammad when a youth, on account of his fair and honourable bearing, which won the confidence of the people.
Aminu ‘l-Bait, one who wishes to perform the pilgrimage to Makkah.
Based on Hughes, Dictionary of Islam