What’s the difference? Serious question. I actually believe the “couvillion” is what couyons incorrectly call a “courtboullion” but I’l let y’all decide.
Coviillion has no tomatoes of any kind. Dad would only make with it with turtle or gar fish. Sauce piquante we made with tomatoe paste and shellfish. Beyond that the recipes we used were similar...onions, garlic, bell pepper and cayenne. Of course both ate over rice.
Etouffee is made with shellfish and eaten over rice. Just saying. And I have eaten squirrel sauce piquante.
For me it’s almost opposite. What we call a sauce piquante has little tomato sauce and more of a browning of meat like squirrel, turtle, etc. It’s more of what I call a “brown gravy” really. I had a baseball coach we would camp with who made a dam good sauce piquante when I was young but do:t remember how he made it.
couvillion and court bouillon refer to the same thing in Louisiana although the "same thing" is cooked 10 different ways. I have always had it with tomatoes or tomato sauce.
Certainly ettoffee is eaten with shellfish and over rice. But sauce piquante is not made with a roux. And I have eaten etouffee with and without a roux. I like them both equally.