noun
mystery; strange event; mysterious affair
Refers to an event or matter that is puzzling, inexplicable, or eerie. Often used in literary or narrative contexts.
その古い屋敷では、夜な夜な怪事が起こるという噂だ。
Rumor has it that strange events occur night after night in that old mansion.
彼は数々の怪事を解決してきた名探偵だ。
He is a famous detective who has solved many mysterious cases.
Compound of 怪 (kai, 'mysterious') and 事 (ji, 'matter, event'). The exact historical derivation is uncertain, but the spelling is conventionally associated with the meaning.