The Collaborative International Dictionary of English v.0.48:

Loess \Loess\ (l[~e]e), 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.
   [1913 Webster]

WordNet (r) 3.0 (2006):

loess
    n 1: a fine-grained unstratified accumulation of clay and silt
         deposited by the wind

Moby Thesaurus II by Grady Ward, 1.0:

35 Moby Thesaurus words for "loess":
   alluvion, alluvium, ash, cinder, clinker, debris, deposit,
   deposition, deposits, detritus, diluvium, draff, dregs, drift,
   dross, ember, feces, froth, grounds, lees, moraine, offscum,
   precipitate, precipitation, scoria, scree, scum, sediment,
   settlings, silt, sinter, slag, smut, soot, sublimate