The term 'endless years' can be represented by two crossword solutions: EON (3 letters) and AEON (4 letters). EON is an abbreviation for an immeasurably long period of time, often used to refer to a geological period or an age. AEON is a Greek word meaning an immeasurably long period of time, often used to refer to eternity or the afterlife. Both terms are used to describe a period of time that is so long that it cannot be measured.