When something is cautionary, it’s meant to be a warning to you. Your parents might be fond of telling cautionary tales, like the one about the girl who got electrocuted sticking a knife into the toaster.
While driving, look for cautionary signs warning you of potential danger: falling rocks, kids crossing, hidden driveway. You might use cautionary words: “Watch your step! There’s glass all over the floor!” Don’t confuse cautionary with cautious, which means trying to avoid danger. Tell a cautionary tale about someone drowning because he swam too far out into the ocean and an overly cautious kid might decide never to swim again.