This is the 1043rd most frequent Polish word.
amerykański
"Amerykański" means "American" in English.
Here, 'amerykański' is used as an adjective to describe the origin of the car, indicating that it is from America or related to America.
Ten samochód jest amerykański.
This car is American.
In this instance, 'amerykańska' modifies 'kultura' (culture), showing an association or characteristic related to America, again functioning as an adjective.
Czy podoba Ci się amerykańska kultura?
Do you like American culture?
In this sentence, 'amerykański' describes 'film' (movie), referring to it as being produced in America or characteristic of America, functioning attributively.