Synonyms for "dog's ages" include a variety of phrases that express a long period of time. Some of these include "an eternity," "forever and a day," "a lifetime," "ages and ages," "an aeon," "a millennium," "a century," "a long time," "a lengthy span," "a protracted period," and "an extended stretch." These phrases convey the idea that something has taken a very long time, which is often the case when referring to "dog's ages." Whether used in a humorous or serious context, these synonyms help to communicate the message clearly and effectively.