Donkey-years is a phrase used to refer to a long period of time. This term originated from the comparison of donkey's lifespan, which is believed to be longer than other domestic animals. There are several synonyms for donkey-years, including aeon, century, eon, era, epoch, generation, lifetime, millennia, eternity, and age. These words are often used interchangeably to describe a significant amount of time that has elapsed or is expected to elapse. Whether it is used in a casual conversation, academic writing, or scientific research, the synonyms for donkey-years accurately capture the immensity and longevity of time.