Use the noun enigma to refer to something that is a puzzle or a mystery. Why do you have to learn difficult words like this? That is an enigma.

Traveling to English from the Greek through the Latin words for "riddle," enigma refers to something or someone that is mysterious, puzzling or difficult to figure out. As a funny-sounding word with an interesting meaning, many things have been named enigma such as a rock band, a video game, a rollercoaster ride, and a very famous coding machine used in World War II.

Definitions of enigma

n something that baffles understanding and cannot be explained

closed book, mystery, secret
Type of:
trouble or confusion resulting from complexity

n a difficult problem

brain-teaser, conundrum, riddle
Type of:
a question raised for consideration or solution

Sign up, it's free!

Whether you're a student, an educator, or a life-long learner, Vocabulary.com can put you on the path to systematic vocabulary improvement.