The term 'long period of time' can be described in a variety of ways. EON (3 letters) is a very long period of time, usually millions of years. AEON (4 letters) is a similar concept, but it is often used to refer to an indefinite period of time. EPOCH (5 letters) is a period of time marked by a particular event or set of characteristics. LONGTERM (8 letters) is a period of time that is longer than the average, but not necessarily indefinite. LONGDISTANCE (12 letters) is a period of time that is longer than usual, but not necessarily indefinite. All of these terms can be used to describe a long period of time.