The phrase "hadst big mouth" can mean that someone talks too much or is overly confident. However, there are several antonyms that can be used to describe someone who is reserved, cautious, or humble. For example, someone who is humble may be described as modest, meek, or unassuming. Alternatively, a reserved individual may be described as quiet, discreet, or introverted. Finally, a cautious person may be described as careful, wise, or prudent. As with any language, choosing the right word depends on the context and intended meaning, but exploring antonyms can help create a more nuanced and descriptive picture of a person or situation.