: strange, unknown, or difficult to understand
the mysterious ways of nature
We heard a mysterious noise outside our tent.
He died under mysterious circumstances.
A mysterious illness has been spreading through the city.
There's something mysterious about that old woman.
Her behavior was very mysterious.
Note: Mysterious people are often interesting because many things are not known about them.
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“Mysterious.” Merriam-Webster.com Simple Definition, Merriam-Webster, https://www.merriam-webster.com/simple/mysterious. Accessed 23 Jun. 2026.
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