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riddle; puzzle; enigma; mystery
enigmatic; mysterious
彼の失踪は今でも謎のままになっている。
His disappearance remains a mystery even now.
彼は時折人前から姿を消し、戻ってきても謎の不在について語ろうとはしなかった。
He would occasionally vanish from before others, and even when he returned he would not speak of his mysterious absences.
科学者がその謎を解明しようとしている。
Scientists are trying to solve that mystery.