1A riddle or puzzle to solve for fun, or something mysterious whose cause or true nature is unclear; a mystery.
子供たちはなぞなぞを出し合って遊んだ。
The children played by taking turns giving each other riddles.
事件の真相はまだ謎のままだ。
The truth behind the incident is still a mystery.
この機械が突然止まった理由は謎だ。
Why this machine suddenly stopped is a mystery.
2Enigmatic or mysterious in nature — used to modify a noun in the pattern '謎の〜' or '謎めいた〜' (mysterious ~).
謎の人物が夜中に屋敷を訪れたという。
It's said a mysterious figure visited the mansion in the middle of the night.
古い日記には謎の記号が書かれていた。
The old diary had mysterious symbols written in it.
彼女の突然の辞職は謎めいていて、誰も理由を知らない。
Her sudden resignation was mysterious, and no one knows the reason.