The Collaborative International Dictionary of English v.0.48:

Simoom \Si*moom"\, Simoon \Si*moon"\, n. [Ar. sam?m, fr. samma
   to poison. Cf. Samiel.]
   A hot, dry, suffocating, dust-laden wind, that blows
   occasionally in Arabia, Syria, and neighboring countries,
   generated by the extreme heat of the parched deserts or sandy
   plains.
   [1913 Webster]

WordNet (r) 3.0 (2006):

simoon
    n 1: a violent hot sand-laden wind on the deserts of Arabia and
         North Africa [syn: simoom, simoon, samiel]