The word "timetested" is often used to describe something that has withstood the test of time and proven to be reliable or effective. However, there are many other ways to express this idea using synonyms. Some possible options include "proven," "tried-and-true," "established," "veteran," "settled," "tested," "trusted," "reliable," "enduring," "time-honored," and "well-worn." Each of these words has its own nuances and connotations, so it's important to choose the one that best fits the specific context and desired tone. Regardless of the choice, using synonyms can add variety and depth to one's writing.