There are several antonyms for the word "untriedest." One of the most fitting antonyms is "experienced." Other opposites of untriedest include "proven," "tested," "well-tried," "well-established," and "established." These antonyms all suggest a level of familiarity and demonstrated success, whereas untriedest implies something that is completely new and untested. In a sentence, you might say "the untriedest candidate was hired," meaning that the person was the least experienced and proven of all the candidates. Conversely, saying "the most well-established candidate was hired" would indicate that the person had the most experience and had been proven successful in the past.