Source : Webster's Revised Unabridged Dictionary (1913)

Loess \Loess\, n. [G. l["o]ss.] (Geol.)
   A quaternary deposit, usually consisting of a fine yellowish
   earth, on the banks of the Rhine and other large rivers.

Source : WordNet®

loess
     n : a fine-grained unstratified accumulation of clay and silt
         deposited by the wind