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):

moistening
    n 1: the act of making something slightly wet [syn:
         moistening, dampening]

Moby Thesaurus II by Grady Ward, 1.0:

37 Moby Thesaurus words for "moistening":
   affusion, aspergation, aspersion, baptism, bath, bathing, bedewing,
   dampening, damping, deluge, dewing, drenching, drowning, flooding,
   hosing, hosing down, humectant, humidification, immersion,
   inundation, irrigation, irrigational, irriguous, laving, rinsing,
   soaking, sopping, sparging, spattering, splashing, splattering,
   spraying, sprinkling, submersion, swashing, watering, wetting