Rein and reign

Grammar Gremlins: 'Rein' and 'reign' can be tricky
By Don Ferguson of the Knoxville News Sentinel
Sunday, August 19, 2007

Is it “free rein” or “free reign”?
In the expression “free rein,” the “allusion is to horses, not to kings and queens,” according to Garner’s Modern American Dictionary.
“But some writers have apparently forgotten this allusion,” the author writes.
Among the many words that sound alike, “rein” and “reign” perhaps head the list of those most often confused.
“Rein” is the correct form for “to restrain,” as in pulling on the reins of a horse to slow it down.
Therefore, a person with “free rein” has no restraints on him.
“Reign” means the period of rule or dominance, usually of a monarch.