1. Plural of eustacy; sustained changes in sea level relative to the continental crust, caused by factors such as changes in ocean volume or basin shape.
Usage: geology; technical term; also spelled 'eustasies'

Examples

• Geologists study eustacies to understand how ocean levels have changed over millions of years.
• The eustacies of the Pleistocene epoch were driven by glacial advance and retreat.
• Multiple eustacies have shaped coastal landscapes throughout Earth's history.
• Climate change may trigger new eustacies in the coming centuries.