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riddle; puzzle; enigma
子どもたちがなぞなぞを出し合って遊んだ。
The children played by taking turns asking riddles.
このなぞなぞの答えが分からない。
I cannot figure out the answer to this riddle.
先生がなぞなぞで授業を盛り上げた。
The teacher livened up the class with riddles.