Definition of medieval adjective from the Oxford Advanced American Dictionary

medieval

adjective (also mediaeval)
/ˌmidiˈivl; ˌmɛdiˈivl; ˌmɪdˈivl/
 
[usually before noun]
 
connected with the Middle Ages (about AD 1000 to AD 1450)
medieval architecture/castles/manuscriptsthe literature of the late medieval period