Kitāb al-ʿAyn (Arabic: كتاب العين) is the first Arabic language dictionary and one of the earliest known dictionaries of any language. It was compiled in the eighth century by al-Khalil ibn Ahmad al-Farahidi. The letter ayn (ع) of the dictionary's title is regarded as phonetically the deepest letter in the Arabic alphabet. In addition the word ayn carries the sense of 'a water source in the desert'. Its title "the source" alludes also to the author's interest in etymology and tracing the meanings of words to their Arabic origins. Al-Farahidi, who was from the Basra School, chose an unusual arrangement that does not follow the alphabetical order familiar today as the standard dictionary format. Al-Farahidi devised a phonetic system that followed the pattern of pronunciation of the Arabic alphabet. According to this system the order begins with the deepest letter in the throat, the letter ﻉ (ayin), and ends with the last letter pronounced by the lips, that being م (mim). Due to ayin's position as the innermost letter to emerge from the throat, he viewed its origins deep down in the throat as a sign that it was the first sound, the essential sound, the voice and a representation of the self.The original manuscript copy by al-Farahidi is believed to have survived up until the fourteenth century when it seems to have disappeared. However summarized copies by the al-Andalus lexicologist Abu Bakr al-Zubaydi (d. 989), were circulating there by the tenth century. Source: Wikipedia (en)