Most loudmouth is a phrase often used to describe someone who is very talkative and outspoken. However, there are several antonyms that express the opposite meaning. Some relevant antonyms include reticent, introverted, shy, quiet, taciturn, restrained, and reserved. These terms describe people who are more reserved in their speech and do not immediately share their opinions or thoughts. Such persons are often more circumspect and selective with their words, preferring to listen and observe first before speaking. By contrast, most loudmouth people tend to dominate conversations, monopolize discussions, and talk more than others. Therefore, using antonyms can help convey a more nuanced description of people's personality and communication styles.