This is the 2873rd most frequent Turkish word.
hırvat
Croat; a person from Croatia.
In this sentence, 'Hırvat' is used as a noun to describe a person of Croatian nationality.
O bir Hırvat, Zagreb'de yaşıyor.
He is a Croatian and lives in Zagreb.
Here, 'Hırvat' functions as an adjective to describe the type of culture, Croatian culture.
Hırvat kültürü hakkında bir kitap aldım.
I bought a book about Croatian culture.
In this case, 'Hırvat' is used as an attributive adjective to qualify the noun 'arkadaşım' (my friend).