The Collaborative International Dictionary of English v.0.48:

Sediment \Sed"i*ment\, n. [F. s['e]diment, L. sedimentum a
   settling, fr. sedere to sit, to settle. See Sit.]
   1. The matter which subsides to the bottom, from water or any
      other liquid; settlings; lees; dregs.
      [1913 Webster]

   2. (Geol.) The material of which sedimentary rocks are
      formed.
      [1913 Webster]

WordNet (r) 3.0 (2006):

sediment
    n 1: matter that has been deposited by some natural process
         [syn: sediment, deposit]
    v 1: deposit as a sediment
    2: settle as sediment

Moby Thesaurus II by Grady Ward, 1.0:

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