"From way back" is an idiomatic expression for something that has existed for a long time or is deeply rooted in history. There are several synonyms that can be used to convey a similar meaning, including "since time immemorial," "through the ages," "since the dawn of time," and "since ancient times." These phrases suggest something that has been present for a very long time and has a rich history behind it. Other synonyms that can be used to convey the same idea include "time-honored," "historic," and "traditional." All of these words convey a sense of rootedness in the past and suggest something that has stood the test of time.