Source : Webster's Revised Unabridged Dictionary (1913)

Khamsin \Kham*sin`\, n.
   Same as {Kamsin}.

Kamsin \Kam*sin"\, Khamsin \Kham*sin"\, n. [Ar. khams[=i]n, fr.
   khams[=u]n, oblique case khams[=i]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}.]

Source : WordNet®

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