The term "full-mouthed" is typically used to describe someone who speaks loudly or with great emphasis. When looking for antonyms to this word, one might consider phrases that describe someone who speaks softly, timidly, or with hesitation. Some possible antonyms for "full-mouthed" might include "soft-spoken," "shy," "reticent," "mumbling," "inarticulate," or "unassertive." Other phrases that might be used to describe someone who is not "full-mouthed" could include "reserved," "introverted," "withdrawn," or "subdued." Regardless of which antonyms one chooses to use, it is important to consider the context in which the term is being used in order to find the most appropriate words to convey the desired meaning.