The Big Mac is a popular hamburger sandwich created by McDonald's. It consists of three main components: onions (6 letters), BUN (3 letters) and patty (5 letters). Onions are a type of vegetable that are often used as a topping on burgers. The BUN is a type of bread that is used to hold the burger together. The patty is a flat piece of ground beef that is cooked and served between the BUN and the onions.