The Collaborative International Dictionary of English v.0.48:

Hyksos \Hyk"sos\, n. [Gr. ?, fr. Egypt. hikshasu chiefs of the
   Bedouins, shepherds.]
   A dynasty of Egyptian kings, often called the Shepherd
   kings, of foreign origin, who, according to the narrative of
   Manetho, ruled for about 500 years, forming the XVth and
   XVIth dynasties. It is now considered that the XVIth is
   merely a double of the XVth dynasty, and that the total
   period of the six Hyksos kings was little more than 100
   years. It is supposed that they were Asiatic Semites.
   [Webster 1913 Suppl.] Hylaeosaur