The phrase "gives a piece of one's mind" typically implies that someone is expressing their anger or frustration towards another person. Antonyms, or words with opposite meanings, for this phrase could include "restrain oneself," "hold back," or "keep quiet." These words might suggest a more measured or calm approach to a situation, rather than immediately lashing out. Other antonyms could include "forgive," "forget," or "move on," which imply a willingness to let go of a grievance or issue without confrontation. Ultimately, the choice of antonym will depend on the context and the speaker's intentions in the given situation.