The term "one-horse" originally referred to a small carriage that was pulled by a single horse. Over time, the term evolved to describe anything that was small or insignificant. If you're looking for synonyms for "one-horse," there are several options to consider. For example, you might use the term "minuscule" to describe something that is incredibly small or insignificant. Alternatively, you could use the word "inconsequential" to describe something that has little or no importance. Other options include "petty," "trivial," "insignificant," and "unimportant." Whatever word you choose, just make sure it accurately conveys the intended meaning.