The term "most newish" implies something that is recent or modern in nature. Antonyms for this phrase could include terms like "dated," "old-fashioned," "archaic," or "antique." These words all suggest something that is old, outdated, or no longer relevant in modern times. Other antonyms that could be used for "most newish" might include "classic," "vintage," or "retro," which imply something that is older but still has value or relevance in contemporary culture. Ultimately, the antonyms for "most newish" all suggest a sense of history, age, or timelessness, in contrast to the newness that the phrase connotes.