From BiblePortal Wikipedia

Webster's Dictionary [1]

(n.) The head of an Arab family, or of a clan or a tribe; also, the chief magistrate of an Arab village. The name is also applied to Mohammedan ecclesiastics of a high grade.

Cyclopedia of Biblical, Theological and Ecclesiastical Literature [2]

(Arabic for elder), a title of reverence, applied chiefly to a learned man or a reputed saint, but also used sometimes as an ordinary title of respect, like the European Mr., Herr, etc., before the name. It is, however, only given to a Moslem. The term is also applied to heads of Mohammedan monasteries, and to the higher order of religious preachers. The sheik of Mecca, by virtue of his supposed descent from the prophet, levies a kind of tribute on all the pilgrims to the Kaaba.