A roundabout is a:

• A straight intersection with four stop signs
• A square intersection with traffic lights in all directions
• A round intersection with a small diameter that makes drivers decrease speed, normally to 30 mph or less.
  Explanation:

  "A "roundabout" is a round intersection with a small diameter that makes drivers decrease speed, normally to 30 mph or less. "
• A triangular intersection with yield signs in all directions