Even though most of us don't use horses or buggies as our main transportation these days, our language still has horse-related idioms, which writers sometimes mix up. One idiom that came up in a story I edited this week was rendered "full reign," to imply that something was unhampered. In fact, the idiom is "full rein" as in allowing a horse to gallop all out. "Free rein" is a variation of that. Sometimes, writers report that efforts have been made to "reign in" an activity. That, too, should be "rein," as when a rider pulls up on the horse's[.....]