Definition of "brightener"

brightener

noun
plural brighteners
1. One who or that which brightens.
  Quotations
  Country air in the fields, or in gardens, when breathed at proper hours, is an excellent bracer of the nerves, and a sure brightener of the complexion.
  1830, The Mirror of the Graces: Or, The English Lady's Costume, page 27
  Chirol's own advice was simple: get the Russian agreement signed. March, month of change, brightener of days and moods, brought that action notably closer.
  2006, Linda Fritzinger, Diplomat Without Portfolio: Valentine Chirol, His Life and "The Times"
2. A chemical agent that absorbs ultraviolet and violet light and re-emits blue light by fluorescence, used to make fabric or paper look whiter.
3. (metallurgy) Any substance added to an electrolytic bath to yield a brighter electroplated surface.