Source : Webster's Revised Unabridged Dictionary (1913)

Sombrero \Som*bre"ro\, n. [Sp., from sombra shade. See
   {Sombre}.]
   A kind of broad-brimmed hat, worn in Spain and in Spanish
   America. --Marryat.

Source : WordNet®

Sombrero
     n 1: one of the islands of Saint Christopher-Nevis
     2: a straw hat with a tall crown and broad brim; worn in
        American southwest and in Mexico