There was a case in Bogle v. Magone, the U.S. Superior Court discussing rather it was LEGAL to eat just an appetizer and call it dinner. The answer was no. They brought up many arguments about the definition of appetizer in this case. The definition of an appetizer is a snack before dinner. there fore an appetizer can not legally be called dinner. They state how restaurants are misleading customers by telling them they can have an appetizer for dinner.

So 117 years ago the Supreme Court states that appetizers are eaten before a meal and, logically, that gastronomical event cannot be the same as the meal that follows.

Referenced from NWLawyer Magazine article Is It Legal to Just Eat Appetizers for Dinner? By David Skeen