Dictionary.com Thesaurus.com

medieval vs. Middle Ages

medieval

[mee-dee-ee-vuhl, med-ee-, mid-ee-, mid-ee-vuhl] / ˌmi diˈi vəl, ˌmɛd i-, ˌmɪd i-, mɪdˈi vəl /

Or mediaeval

adjective

of, pertaining to, characteristic of, or in the style of the Middle Ages.

medieval architecture.
Informal. extremely old-fashioned; primitive.

Middle Ages

plural noun

the time in European history between classical antiquity and the Italian Renaissance (from about 500 a.d. to about 1350): sometimes restricted to the later part of this period (after 1100) and sometimes extended to 1450 or 1500.