What does al- mean?
The definition of al-
Al-. A prefix. (a)
Etym: [AS. eal.]
Defn: All; wholly; completely; as, almighty,almost. (b)
Etym: [L. ad.]

To; at; on; — in OF. shortened to a-. See Ad-.

(c) The Arabic definite article answering to the English the; as, Alkoran, the Koran or the Book; alchemy, the chemistry.