The Collaborative International Dictionary of English v.0.48:

Soil \Soil\ (soil), v. t. [imp. & p. p. Soiled (soild); p. pr.
   & vb. n. Soiling.] [OF. saoler, saouler, to satiate, F.
   so[^u]ler, L. satullare, fr. satullus, dim. of satur sated.
   See Satire.]
   To feed, as cattle or horses, in the barn or an inclosure,
   with fresh grass or green food cut for them, instead of
   sending them out to pasture; hence (such food having the
   effect of purging them), to purge by feeding on green food;
   as, to soil a horse.
   [1913 Webster]

WordNet (r) 3.0 (2006):

soiled
    adj 1: soiled or likely to soil with dirt or grime; "dirty
           unswept sidewalks"; "a child in dirty overalls"; "dirty
           slums"; "piles of dirty dishes"; "put his dirty feet on
           the clean sheet"; "wore an unclean shirt"; "mining is a
           dirty job"; "Cinderella did the dirty work while her
           sisters preened themselves" [syn: dirty, soiled,
           unclean] [ant: clean]

Moby Thesaurus II by Grady Ward, 1.0:

33 Moby Thesaurus words for "soiled":
   bedraggled, befouled, besmirched, blackened, darkened, defiled,
   dirtied, discolored, drabbled, draggled, fouled, foxed, foxy,
   impure, indecent, inky, maculate, murky, smirched, smoky, smudged,
   spotted, stained, stigmatic, stigmatiferous, stigmatized, sullied,
   tainted, tarnished, unchaste, unclean, unvirginal, unvirtuous