The term SIGNIFICANT TIME SPANS can be broken down into two crossword solutions: ERAS (4 letters). An era is a period of time in history that is marked by certain characteristics or events. ERAS are typically used to divide up long periods of time, such as centuries or millennia, and are often named after a significant event or person. For example, the Middle Ages is an era that lasted from the 5th to the 15th century, and is often associated with the fall of the Roman Empire and the rise of feudalism.