Duden, Das große Fremdwörterbuch:
Kamsin u. Chamsin der; [..] <aus arab. hamsīn "(Wind von) fünfzig (Tagen)"> : trockenheißer Sandwind in der ägyptischen Wüste (Meteor.)' vgl. Gibli u. Schirokko

Wörterbuch der deutschen Sprache:
Kam|sin [m. 1] → Chamsin
Cham|sin [kam– auch xam– m. 1; in Ägypten und Arabien] heißer Wüstenwind mit driftendem Sand und Staub; <auch> Kamsin [arab., ”fünfzig“, da er in den 50 Tagen nach der Frühlings–Tagundnachtgleiche weht]

http://unabridged.merriam-webster.com
Main Entry: kham·sin
Variant(s): also kham·seen or cham·sin
Function: noun
Etymology: Arabic (rīh al-) khamsīn the wind of the fifty (days between Easter and Pentecost)
: a hot southerly Egyptian wind coming from the Sahara usually in the spring and often carrying fine particles of sand <the khamsin ... has been known to take paint off cars and force fine sand into camera shutters -- G.E.Edgerton> -- compare SIROCCO

http://www.bartleby.com/61/92/K0049200.html
The American Heritage® Dictionary of the English Language: Fourth Edition.
khamsin
SYLLABICATION: kham·sin
NOUN: A generally southerly hot wind from the Sahara that blows across Egypt from late March to early May.
ETYMOLOGY: Arabic (rīh al-)hamsīn, (wind of the) 50 (days), khamsin, from oblique case of hamsūn, fifty, from hams, five.

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