Source : Webster's Revised Unabridged Dictionary (1913)

Soil \Soil\, v. t. [imp. & p. p. {Soiled}; 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.

Source : WordNet®

soiling
     n : the act of soiling something [syn: {soilure}, {dirtying}]