Noun

1. A period of five years.
   • 1835, Edgar Allen Poe, ‘Morella’, Tales of Mystery and Imagination, Folio Society 2007, p. 31:

     Thus passed away two lustra of her life, and, as yet, my daughter remained nameless upon the earth.

   • 1985, John Fowles, A Maggot:

     Q. Now, sir, if you would be so kind as to guess upon his age. A. Forty five years are certain. I would guess a lustrum more.