Hold Your Horses

Almost certainly rooted in the literal difficulty of controlling real horses, but exactly which horses is less clear. The earliest documented form is American, written as "hold your hosses" ("hoss" being period slang for horse) from 1843 onward. One popular theory ties it specifically to New York's Erie Canal, where horse teams towing barges along the towpath needed a shouted warning to manage right of way when passing each other. It's a plausible, well-fitting story for the period, but it's just as likely the phrase simply grew from the everyday difficulty of controlling any horse, canal-side or not.