Definition of "lightness"

lightness¹

/ˈlaɪtnəs/

noun
countable and uncountable, plural lightnesses
1. (uncountable) the condition of being illuminated
2. (uncountable) the relative whiteness or transparency of a colour
3. (countable) The product of being illuminated.

lightness²

/ˈlaɪtnəs/

noun
uncountable
1. The state of having little (or less) weight, or little force.
  Quotations
  The unique chassis design is largely the secret of the lightness of the locomotive.
  1960 January, “The Swindon Type "4" diesel-hydraulic units”, in Trains Illustrated, page 39
2. Agility of movement.
3. Freedom from worry.
  Quotations
  In the lightness of my heart I sang catches of songs as my horse gayly bore me along the well-remembered road.
  1852, Mrs M.A. Thompson, “The Tutor's Daughter”, in Graham's American Monthly Magazine of Literature, Art, and Fashion, page 266
4. Levity, frivolity; inconsistency.
  Quotations
  Seneca […] accounts it a filthy lightness in men, every day to lay new foundations of their life, but who doth otherwise?
  1624, Democritus Junior [pseudonym; Robert Burton], The Anatomy of Melancholy: […], 2nd edition, Oxford, Oxfordshire: Printed by John Lichfield and James Short, for Henry Cripps