The phrase "blow whistle" typically implies an act of revealing or reporting misbehavior. The antonyms for this phrase can include phrases such as keep quiet, ignore, or cover up. To keep quiet means to not say anything about a situation or behavior, whereas ignoring something means to not acknowledge it at all. Covering up involves intentionally hiding or disguising something. Antonyms for "blow whistle" may also include phrases such as support, encourage, or defend, which suggest that one is standing by a person or behavior rather than reporting it. The opposite meaning could be conveyed by phrases like "protect," "shield," and "conceal.