The term 'Many Eras' can be broken down into two crossword solutions: EON (3 letters) and EONS (4 letters). An EON is an immeasurably long period of time, typically used to refer to the longest divisions of geological time. An EON is divided into eras, which are further divided into periods, epochs, and ages. An EON is the largest unit of geological time, and is usually measured in billions of years. EONS is simply the plural form of EON.