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Webster 1913 Edition

Noun.

The quality or state of being moist.

Noun.

Dampness; a small degree of wetness.

moistness ‎(countable and uncountable, plural moistnesses)

The property of being moist.
(obsolete) Moisture.
- 1603, John Florio, translating Michel de Montaigne, Essayes, London: Edward Blount, OCLC 946730821, II.12:
  The moistnesse which the roote of a tree suckes becomes a trunke, a leafe, and fruite: And the aire being but one, applied unto a trumpet, becommoth diverse in a thousand sorts of sounds.

moistness