IPA: //mɪˈdiːvəlɪst//
KK: /mɪˈdiːvəlɪst/
A person who studies or is an expert in the culture, history, and arts of the Middle Ages.
The medievalist gave a fascinating lecture on the architecture of cathedrals from that era.
Medievalist → It is formed from "medieval" (from Latin *medium aevum*, meaning the middle ages) and "-ist" (meaning one who practices or is concerned with). A medievalist is someone who studies or specializes in the Middle Ages.
Think of someone who is focused on the 'middle ages' ('medieval') and the '-ist' indicates a person who studies or practices that field.