This is the 473rd most frequent Russian word.
китай
China.
The word 'Китай' is used here as a proper noun to refer to the country China.
Я мечтаю посетить Китай в следующем году.
I dream of visiting China next year.
The word 'китайский' is used as an adjective to describe the language being studied, meaning 'Chinese'.
Мой друг изучает китайский язык в университете.
My friend is studying the Chinese language at the university.
The word 'китайской' is an adjective derived from 'Китай', used here to describe the type of cuisine (Chinese).