Medieval

google

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early 19th century: from modern Latin medium aevum ‘middle age’ + -al.

wiktionary

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From French médiéval(“medieval”), from Latin medium(“middle”) + aevum(“age”).

etymonline

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medieval (adj.)

"pertaining to or suggestive of the Middle Ages," 1825 (mediaeval), coined in English from Latin medium "the middle" (from PIE root *medhyo- "middle") + aevum "age" (from PIE root *aiw- "vital force, life; long life, eternity").