A Grand Duchy is a state ("nation" in common, modern language) in which the Head of State (the ruler) is a Grand Duke.
Similarly, a Duchy is a state where the ruler is a Duke
Because the head of state is a Grand Duke. It is the same thing for France. France is officialy called the French Republic, because it is a republic. The US and the UK are one of the rare countries...
They have grand beaches, so they swim and boating. They have casinos and clubs so they party. They aren't far from France and Paris is just down the road. They also aren't far from Germany and good...
A constitutional law is a law that obeys the constitution, an non constitutional law is one that goes against what it said. That answer is vague, so you should look into it more.