noun (n)

• the property possessed by a slope that is very gradual(noun.attribute)

  Synonym:
  gentleness
  Antonym:
  abruptness, precipitousness, steepness
  

  source: wordnet30
• the quality of being gradual or of coming about by gradual stages(noun.attribute)

  Synonym:
  graduality
  

  source: wordnet30
• The quality or state of being gradual; regular progression or gradation; slowness.(noun)

  source: webster1913