Definition of lustrum in English:

lustrum

noun

historical, literary
  • A period of five years.

    • ‘The book is dedicated to Nygren's wife Irmgard "in thankfulness for seven lustrums of theological cooperation."’
    • ‘37 years ago my first secretary was a lady who has remained my friend for nearly 8 lustrums (4 decades) and today is a leading lady lawyer in Los Angeles who has never lost a case in court.’

Origin

Late 16th century: from Latin, originally denoting a purificatory sacrifice after a quinquennial census.

Pronunciation:

lustrum

/ˈlʌstrəm/