The Collaborative International Dictionary of English v.0.48:

Moisten \Mois"ten\, v. t. [imp. & p. p. Moistened; p. pr. &
   vb. n. Moistening.]
   1. To make damp; to wet in a small degree.
      [1913 Webster]

            A pipe a little moistened on the inside. --Bacon.
      [1913 Webster]

   2. To soften by making moist; to make tender.
      [1913 Webster]

            It moistened not his executioner's heart with any
            pity.                                 --Fuller.
      [1913 Webster]

WordNet (r) 3.0 (2006):

moisten
    v 1: make moist; "The dew moistened the meadows" [syn:
         moisten, wash, dampen]
    2: moisten with fine drops; "drizzle the meat with melted
       butter" [syn: drizzle, moisten]

Moby Thesaurus II by Grady Ward, 1.0:

32 Moby Thesaurus words for "moisten":
   asperge, bedew, bespatter, besprinkle, dabble, damp, dampen, dash,
   dew, douche, hose, hose down, humect, humectate, humidify,
   irrigate, paddle, slobber, slop, slosh, sparge, spatter, splash,
   splatter, sponge, spray, sprinkle, swash, syringe, water, wet,
   wet down