The term 'REALLY LONG TIME' can be represented by several words in a crossword puzzle. EON (3 letters) is a very long period of time, usually millions of years. EONS (4 letters) is the plural form of EON and also refers to a very long period of time. AEON (4 letters) is another word for an EON, but it is more commonly used in literature. AGES (4 letters) is a much shorter period of time than an EON, but still a very long time. MILLENNIA (9 letters) is a period of time that is even shorter than an age, but still much longer than a regular human lifespan.