Division of time is a concept used to measure the passage of time. EON, which is a three letter word, is a very long period of time, usually millions of years. EPOCH, which is a five letter word, is a period of time marked by certain events or characteristics. AEON, which is a four letter word, is another term for an EON. ERA, which is a three letter word, is a period of time marked by certain events or characteristics. MINUTE, which is a six letter word, is a unit of time equal to 60 seconds. Year, which is a four letter word, is a unit of time equal to 365 days.