The Collaborative International Dictionary of English v.0.48:

Drench \Drench\, v. t. [imp. & p. p. Drenched; p. pr. & vb. n.
   Drenching.] [AS. drencan to give to drink, to drench, the
   causal of drincan to drink; akin to D. drenken, Sw.
   dr[aum]nka, G. tr[aum]nken. See Drink.]
   1. To cause to drink; especially, to dose by force; to put a
      potion down the throat of, as of a horse; hence. to purge
      violently by physic.
      [1913 Webster]

            As "to fell," is "to make to fall," and "to lay," to
            make to lie." so "to drench," is "to make to drink."
                                                  --Trench.
      [1913 Webster]

   2. To steep in moisture; to wet thoroughly; to soak; to
      saturate with water or other liquid; to immerse.
      [1913 Webster]

            Now dam the ditches and the floods restrain;
            Their moisture has already drenched the plain.
                                                  --Dryden.
      [1913 Webster]

WordNet (r) 3.0 (2006):

drenching
    n 1: the act of making something completely wet; "he gave it a
         good drenching" [syn: drenching, soaking, souse,
         sousing]

Moby Thesaurus II by Grady Ward, 1.0:

32 Moby Thesaurus words for "drenching":
   brewing, dampening, drench, ducking, dunking, humectant,
   imbruement, imbuement, impregnation, infiltration, infusion,
   injection, irrigational, irriguous, leaching, lixiviation,
   maceration, moistening, percolation, permeation, pulping,
   saturation, seething, soak, soakage, soaking, sopping, souse,
   sousing, steeping, watering, wetting