IPA: /mɪˈstɪəriəsli/
KK: /mɪˈstɪrɪəsli/
In a way that is difficult to understand or explain, often causing curiosity or wonder.
The lights turned off mysteriously, leaving everyone in the dark.
Mysteriously → It is formed from "mystery" (from Greek "mystērion", meaning a secret or hidden thing) and the suffix "-ously" (meaning in a manner of). The word "mysteriously" means in a manner that is secretive or difficult to understand.
Think of something that is a 'secret' ('mystery') and happening 'in a manner' ('-ously') that is hard to grasp. This helps you remember that 'mysteriously' describes something that is done in a secretive or puzzling way.