Antonyms for the phrase "make oneself heard" refer to the actions that make someone unable to get their voice heard. These could range from keeping silent, staying quiet, or avoiding speaking up. They could also include behaviors like muttering or speaking in a low tone, speaking incoherently, or speaking too fast or too soft. Other words that could be used as antonyms to "make oneself heard" include hiding, concealing, or cloaking one's voice, which might denote some degrees of dishonesty or intentionally hiding one's real intentions or feelings. Overall, antonyms for making oneself heard are behaviors that involve silence, concealment, or ineffectiveness in communication.