Jump the gun is a phrase that means to act prematurely, before all the facts are known or before the appropriate time has arrived. There are several synonyms for this expression. One such synonym is to be hasty, which refers to a tendency to act impulsively or without sufficient consideration. Another synonym is to be impetuous, which means to act without forethought or caution. A third synonym is to be rash, which implies a reckless disregard for consequences. Regardless of which synonym one uses, the underlying meaning is the same: to act before it is time to do so, often to one's detriment.