Antonyms are words that have opposite meanings to each other. For the phrase "biting nails," some possible antonyms could be "relaxed," "calm," or "composed." These words suggest a sense of ease and tranquility, which is the opposite of the tension and anxiety often associated with nail-biting. Other antonyms might include "unworried," "unperturbed," or "unruffled," which convey a similar sense of ease and lack of concern. Whatever the antonym, it should be a word that evokes a sense of calm and peacefulness, providing a counterbalance to the nervous energy of biting one's nails.