From Longman Dictionary of Contemporary Englishmysteriousmys‧te‧ri‧ous /mɪˈstɪəriəs $ -ˈstɪr-/ ●●○ adjective 🔊 🔊 1MYSTERIOUSmysteriousevents or situations are difficult to explain or understand 🔊 The police are investigating the mysterious deaths of children at the hospital. 🔊 Benson later disappeared in mysterious circumstances. 🔊 There’s something mysterious going on.► see thesaurus at strange2MYSTERIOUSa mysterious person is someone who you know very little about and who seems strange or interesting syn enigmatic 🔊 I decided to find out more about my mysterious new neighbour. 🔊 a mysterious stranger3TELL A SECRETsomeone who behaves in a mysterious way says very little about what they are doing syn secretivemysterious about 🔊 Helen’s being very mysterious about her plans. 🔊 She hid her thoughts behind a mysterious smile. —mysteriously adverb 🔊 Jackson had mysteriously disappeared.THESAURUSmysterious difficult to explain or understand, and often strange or slightly frighteningthe mysterious disappearance of ships in the waters of the Bermuda TriangleWhat’s that mysterious noise?puzzling difficult to explain or understandAt first this must seem a puzzling question.I found her attitude deeply puzzling.bafflingimpossible to understand, so that you feel very confusedIt was a baffling case.Like many people, I find theoretical physics baffling.inexplicable formal impossible to explainFor some inexplicable reason her mind went completely blank.Some things in life are inexplicable.enigmatic formal mysterious and difficult to understand, but also often attractive or interesting – used especially about people, their expressions, or things they sayShe gave him an enigmatic smile.an enigmatic remarkcryptic formal having a meaning that is difficult to understand, and is not expressed in a cleardirect way – used especially about things that people say or writeI got a rather cryptic message from him.cryptic commentsbe a mystery if something is a mystery, you cannot understand how or why it happensFour years later, his death remains a complete mystery.It’s all a mystery to me.be shrouded/veiled in mystery if an event or a situation, especially one that happened a long time ago, is shrouded in mystery, it is mysterious because no one knows exactly what happenedStone age civilization, veiled in mystery as it is, has provided the greatest challenge to historians.