IPA: //mɪˈdiːvəl//
KK: /mɪˈdiːvəl/
Relating to the Middle Ages, a period in European history from about the 5th to the late 15th century.
The castle was built in a mediaeval style, with tall towers and thick walls.
Mediaeval → It is formed from "media" (from Latin *medium*, meaning middle) and "aevum" (meaning age or era). The term refers to the middle age or period in history, specifically the time between the fall of the Roman Empire and the beginning of the Renaissance.
Think of the word 'middle' ('media') and 'age' ('aevum') to remember that 'mediaeval' refers to the middle ages in history.