Reign -- what a regnant such as a king reigns over. Rein -- what you use to guide a horse Rain -- water that falls from the sky Free reign -- a kingdom where

Reign -- what a regnant such as a king reigns over. Rein -- what you use to guide a horse Rain -- water that falls from the sky Free reign -- a kingdom where people have freedom, but are still under monarchical rule Free rein -- letting go of that which you control a horse with (preferred idiom) Free rain -- rain's default state