1. Plural of lustrum; a period of five years in ancient Rome, or any period of five years.
Usage: historical; formal
2. A ceremonial purification of the Roman people conducted every five years.
Usage: historical; archaic

Examples

• The Roman census was conducted every lustrum, marking the passage of five years.
• Several lustrums passed before the empire saw significant territorial expansion.
• The lustrum ceremony was an important religious and civic event in ancient Rome.
• Historians divided the reign into multiple lustrums to track administrative changes.
• The concept of lustrums influenced how Romans measured and organized historical time.