A type of question that describes something in a difficult and confusing way and has a clever or funny answer. often asked as a game. (Cambridge Dictionary)
Something that is confusing or a problem that is difficult to solve. (Cambridge Dictionary)
A question or statement intentionally phrased so as to require ingenuity in ascertaining its answer or meaning. (Oxford Dictionaries)
A person or thing that is difficult to understand or explain. (Oxford Dictionaries)
A riddle is a puzzle or joke in which you ask a question that seems to be nonsense but which has a clever or amusing answer. (Collins Dictionary)
You can describe something as a riddle if people have been trying to understand or explain it but have not been able to. (Collins Dictionary)
A mystifying, misleading, or puzzling question posed as a problem to be solved or guessed : Conundrum, Enigma. (Merriam – Webster)
Something or someone difficult to understand. (Merriam – Webster)
Riddle: What Disappears as Soon as You Say its Name?
Many Adults Are Stumped By The Horse Riddle – Can You Solve It?