When it comes to synonyms for the phrase "keep something back", several alternatives exist that convey similar meanings. One such synonym is "withhold", which implies the act of intentionally holding something back from others. Similarly, "conceal" suggests the act of hiding or keeping something secret or out of sight. Another synonym for "keep something back" is "restrain", which suggests the act of holding back or controlling one's emotions, actions, or behavior. "Suppress" is another option, implying the act of keeping something in check or restraining oneself from expressing or divulging information. Lastly, "retain" can be used as a synonym, conveying the idea of keeping possession or control over something.