A "loose cannon" is someone who is unpredictable and liable to cause harm or damage. Some synonyms for this phrase include "wild card," "unrestrained," "reckless," and "unpredictable." A person who is a loose cannon can be described as a liability, a hazard, or a danger. They may act impulsively or erratically, making it difficult to rely on them in certain situations. Other synonyms that may apply to a loose cannon include "volatile," "capricious," "uncontrollable," and "disruptive." Ultimately, this type of person can be frustrating, exhausting, or even dangerous to be around, as they can make it challenging to maintain order or stability.