The term 'AGES UPON AGES' can be broken down into four crossword solutions: EON (3 letters), AEON (4 letters), EONS (4 letters), and AEONS (5 letters). EON is a unit of geological time, typically lasting millions of years. AEON is a variant spelling of EON, and is also used to refer to an indefinite period of time. EONS is the plural form of EON, and AEONS is the plural form of AEON. Together, these words describe a very long period of time, or 'AGES UPON AGES'.