A "hundred to one shot" is an idiom that refers to an unlikely event or outcome. However, there are several synonyms for this phrase that can be used interchangeably, such as "long shot," "slim chance," "outside chance," or "dark horse." These terms suggest that something is improbable, and that the odds of it happening are not favorable. Additionally, some people may use the phrase "pipe dream" as a synonym for "hundred to one shot," which implies that the situation being discussed is merely a fanciful or unrealistic idea. Overall, each of these phrases conveys the idea that the outcome being discussed is not something that is likely to occur.