The prefix "neo-" generally refers to something new or modern, so its antonyms can describe things that are old-fashioned, traditional, or outdated. The antonyms for "neo-" include words like "retro," "vintage," and "classic," which evoke a sense of nostalgia or a return to an earlier era. Other antonyms might include terms like "archaic," "antiquated," or "obsolete," suggesting that a particular idea or trend is no longer relevant or useful. Finally, the antonyms for "neo-" could also include words like "established," "conventional," or "mainstream," implying that something has become accepted or normalized over time.