Time periods are a way of measuring the passage of time. AEONS (5 letters) is an extremely long period of time, usually referring to millions of years. ERAS (4 letters) is a longer period of time than a century, but shorter than an aeon. SPANS (5 letters) is a period of time between two points or events. DAYS (4 letters) is a unit of time that is equal to 24 hours. COLONS (6 letters) is a unit of time that is equal to one minute and forty seconds. AGES (4 letters) is a long period of time in history or prehistory. EONS (4 letters) is another word for aeon. YEARS (5 letters) is a unit of time that is equal to 365 days. EPOCHS (6 letters) is a period of time marked by significant changes or developments. DECADES (7 letters) is a period of time that is equal to 10 years.