The Collaborative International Dictionary of English v.0.48:

Khamsin \Kham*sin`\, n.
   Same as Kamsin.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Kamsin \Kam*sin"\, Khamsin \Kham*sin"\, n. [Ar. khams[imac]n,
   fr. khams[=u]n, oblique case khams[imac]n, fifty; -- so
   called because it blows for about fifty days, from April till
   June.]
   A hot southwesterly wind in Egypt, coming from the Sahara.
   [Written also Khamseen.]
   [1913 Webster]

WordNet (r) 3.0 (2006):

khamsin
    n 1: an oppressively hot southerly wind from the Sahara that
         blows across Egypt in the spring