I’d like use today’s entry to talk about a particular bugaboo I have.
"Free rein" is an expression that comes to us from the equestrian world and refers to the rider holding the reins loose so that the horse can move in any direction it would like to go.
This term has made it over to the non-equestrian world and refers to "unrestricted liberty of action or decision," according to Messrs. Merriam and Webster. For example, when a manager assigns a project to an employee and gives the employee free rein to complete it, it means the manager trusts the employee to get the job done and leaves the decisions about how it will be done and the method chosen up to the employee.
In contrast, "free reign" might appear to mean the same thing, but it gets the idiom all wrong. "Reign" is something associated with kings, queens,
jacks, princes and princesses. They’re royalty and can thus reign to their heart’s content. They don’t have to get the approval of anyone to do so, because no one is going to pull the reins in on them. The only people who can draw the reins in them are higher ranking royalty, so a queen can put a stop to whatever a prince or princess is doing. HM Queen Elizabeth II has done that a few times in recent memory.
And let’s not even get into free rain…
Bottom line: "free rein" makes sense, "free reign" doesn’t. Use the former, not the latter.