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):

soiling
    n 1: the act of soiling something [syn: soiling, soilure,
         dirtying]