This is the 1222nd most frequent Polish word.
moskwa
"Moskwa" in Polish means "Moscow," the capital city of Russia.
In this sentence, 'Moskwa' is used as a proper noun referring to the city.
Moskwa to stolica Rosji.
Moscow is the capital of Russia.
Here, 'Moskwie' is the locative form of 'Moskwa', used after the preposition 'w' to indicate location.
Za każdym razem, gdy jestem w Moskwie, odwiedzam Kreml.
Each time I am in Moscow, I visit the Kremlin.
In this case, 'Moskwa' is used in its nominative case as the subject of the sentence.