When something is labeled a "hundred-to-one shot," it means that there is a slim chance of it happening. Synonyms for this phrase include "long shot," "dark horse," and "underdog." These terms are often used in sports and competitions, where the outcome may seem unpredictable. Another synonym that could be used in place of "hundred-to-one shot" would be "unlikely event." It's important to note that while these terms indicate a low probability, they do not necessarily indicate impossibility. Sometimes, against all odds, the underdog can emerge victorious and surprise everyone.