前代未聞
ぜんだいみもん unheard-of; unprecedented
Why it means this
前代 (previous ages) + 未聞 (never heard) — a four-character idiom: 'not heard of in any previous age', unprecedented.
Breakdown
- 前 まえ in front, before
- 代 ダイ substitute, change, convert
- 未 ミ un-, not yet, hitherto
- 聞 ブン hear, ask, listen
Each character links to its full entry — origin story, stroke order, and readings.