(1) An extremity, verge, or border. (2) A letter of the alphabet. (3) A particle in grammar. (4) A dialect of Arabia, or a mode of expression peculiar to certain Arabs. The Qur’an is said to have been revealed in seven dialects (sab’ut ahruf). [QUR'AN.] (5) A term used by the Sufi mystics for the particle of any true essence.
Based on Hughes, Dictionary of Islam