Correct spelling for the English word "schack" is [ʃˈak], [ʃˈak], [ʃ_ˈa_k] (IPA phonetic alphabet).
The word "schack" is derived from the Old Persian word "shāh" which means "king". This term was then passed on to the Arabic language as "shāh" and eventually made its way into various European languages, including English, as "check" in chess.
In the 17th century, the term "schack" was introduced in Swedish, referring to the game of chess. Over time, the pronunciation and spelling of the word slightly changed, but its origin from the Persian "shāh" remains the same.