riddle

B2 · Upper Intermediate Countable noun

n. a person or thing that is very difficult to explain or understand.

n. a person, situation, or thing that is mysterious or puzzling.

“How the ancient stones were moved remains a riddle to this day.”

“The sudden disappearance of the colony remains a historical riddle that continues to baffle archaeologists and researchers alike.”

C2 · Proficiency Countable noun Technical

n. a large tool with a wire mesh used for separating stones from soil or grain from husks.

n. a coarse sieve used for sifting large quantities of material such as gravel, grain, or coal.

“The gardener used a riddle to remove the large rocks from the flower bed.”

“Before the grain could be milled, it was passed through a heavy-duty riddle to ensure all debris and chaff were removed.”