As a verb (meaning to struggle or move clumsily):
* The new student floundered trying to understand the complex math problem.
* After losing his way in the woods, the hiker floundered through the underbrush.
* The company floundered financially after losing its biggest client.
As a noun (meaning a type of flatfish):
* We had delicious flounder for dinner, cooked with lemon and herbs.
* The fisherman caught a large flounder on his line.
* Flounder is a popular fish in coastal regions.