something that baffles understanding and cannot be explained
"how it got out is a mystery"
"it remains one of nature's secrets"
a story about a crime (usually murder) presented as a novel or play or movie
"After binge-watching the new mystery, I can't stop thinking about who actually left the lights on."
Something secret or unexplainable; an unknown.
"The detective stared at the empty room, realizing that every clue led back to a deeper mystery about who really owned the house."
In plain English: A mystery is something that is hard to figure out because there are no clear answers yet.
"The mystery of who stole the cake remained unsolved until we found the clues in the kitchen."
Usage: Use "mystery" to describe something that remains unknown, unexplained, or hidden from understanding. It refers specifically to the state of being enigmatic rather than the act of investigating or solving a puzzle.
The word "mystery" entered Middle English from the Latin mysterium, which originally referred to a secret rite or an initiated one in Ancient Greek culture. It replaced the native Old English term for mystery, bringing with it the sense of something hidden or known only through initiation.