noun (n)

• a rate (usually rapid) at which something happens(noun.attribute)

  Synonym:
  fastness, speed
  

  source: wordnet30
• The quality or state of being swift; speed; quickness; celerity; velocity; rapidity; as, the swiftness of a bird; the swiftness of a stream; swiftness of descent in a falling body; swiftness of thought, etc.(noun)

  source: webster1913