The Collaborative International Dictionary of English v.0.48:

Wetness \Wet"ness\, n.
   1. The quality or state of being wet; moisture; humidity; as,
      the wetness of land; the wetness of a cloth.
      [1913 Webster]

   2. A watery or moist state of the atmosphere; a state of
      being rainy, foggy, or misty; as, the wetness of weather
      or the season.
      [1913 Webster]

   Note: Wetness generally implies more water or liquid than is
         implied by humidness or moisture.
         [1913 Webster]

   3. Sweat or sweating; -- a euphemism. [Colloq.]
      [PJC]

WordNet (r) 3.0 (2006):

wetness
    n 1: the condition of containing or being covered by a liquid
         (especially water); "he confirmed the wetness of the
         swimming trunks" [ant: dryness, waterlessness,
         xerotes]