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]