The phrase "nether regions" typically refers to the private parts of the human body. It is often considered inappropriate or vulgar, and therefore there are few polite antonyms for this phrase. However, some possible alternatives might include more neutral or medical terms. For example, instead of "nether regions," one could use the terms "pelvic area," "genitalia," or "groin." These terms are less likely to be seen as offensive, and can be used in a variety of contexts, such as medical discussions, anatomy lessons, or polite conversation. Regardless of the wording, it is important to be respectful and considerate when discussing sensitive topics related to the body.